The Haggadah presents itself in mythic terms. It's not a commemoration of the exodus or Sinai, but a reliving of those events. Everyone is required to see himself as if he had personally left Egypt. This is the mythic conception of an event: an event is not a discrete instance of something that happened in the past, but it's something that happened in the past and continues to happen in the present, reverberating down through the generations.
The historicity of a myth - whether or not there really was in exodus, whether or not Jewish people really stood in front of Sinai and received the torah - is immaterial to the meaningfulness of the myth. The myth is about the beginning of the Jewish nation. It's about us differentiating ourselves from the dominant culture of the time, “ leaving Egypt,” and forming a unique identity as the Jewish people. It's about the beginning of the Jewish people as a distinct people, and the beginning of Jewish values. Values of defending the downtrodden, for we were once slaves in Egypt, and of giving scholarship and intellectual pursuits high status, for we are the people of the book.
Both the exodus and the Sinai experience are important to this narrative. The exodus establishes the Jewish people as its own entity, but only in a negative sense. It's about what we're not - we're not Egyptians. We're not going to be subsumed the dominant culture. Sinai is about what we are. In a religious sense, it's about the acceptance of the religion of Judaism, of the torah and everything that goes with it. In a cultural sense, it's about the finding who we are: the people of the book. We are the people who value the scholar over the warrior, and who, at least ideally, value scholarship, understanding, and wisdom over wealth and other material good. (This is reflected in the Haggadah, in the depictions of the wise and the wicked sons many historical Haggados as a scholar and a soldier respectively.)
Nietzsche picked up on this, but he took the wrong lesson from it. He called it the slave morality. A morality that stresses justice and equality before the law for all members of the group. A morality that celebrates intellectual over physical achievements. A morality that roots for the underdog. He advocated instead for a morality where the strong do what they can. He may be technically right that the strong can do as they will while others concern themselves with justice and wisdom. But a world where the strong do is they will is the world that most of us would not want to live in. The core values of Judaism contribute to a world that everyone can live in. A world where knowledge progresses and uplift us. A world where we all root for the underdog, where we help each other and everyone ends up better off. While we unfortunately often don't live up to these ideals, it is these ideals, rather than strongman ideals of Nietzsche's ubermensch or the materialistic ideals of a purely consumerist society that shape Jewish culture and have contributed to shaping the cultures we've interacted with.
“The Seder ...is rooted in, and geared to, the particular and specific experience of a particular and specific group. What informs it is not—as is frequently taught and still more often believed—the mere abstract principle of freedom, but the distinctive and concrete process by which a certain people achieved and evinced it. For this reason, it cannot be universalized without losing its essence; to validate it in terms of general principles is to distort its basic spirit and to squeeze out of it the very sap of life. The Seder service—and, indeed, the Passover festival as a whole—is as indissolubly and exclusively Jewish as independence day is American. The fact that both are instinct also with universal ideals no more obliterates their particular natures than does the universal prevalence of marriage obliterate the individual quality and significance of each particular union.”
The story of the exodus is vague. Perhaps deliberately so. Myths, unlike history, are meant to speak through the ages. In an historical account, details are important. We'd want to know which pharaoh Moshe was dealing with. We'd want to know how many soldiers chased the Jewish people into the sea. We would want to know details about how the plagues affected Egyptians personally and the Egyptian empire economically and politically. We get none of these details, because it's not history. It's myth. To focus on such details would be to miss the point. There might be a kernel of truth in the exodus story, or it might just be that Egypt, as the superpower in the region at the time the story developed, made for a natural antagonist. Either way, pharaoh and the Egyptians represent a generic dominant culture. And the exodus and the Sinai experience represent the Jewish experience down through the ages: experiences of living within and sharing in a wider culture while maintaining our own, of differentiating ourselves from the dominant culture, and of clinging to love of learning and justice that runs through our own culture.
It also reflects an ongoing experience of adopting elements of those cultures in which we found ourselves and modifying them for our own use. While I don't think this is the original meaning, we can read the passage about the Jewish people taking Egypt's wealth with them as a metaphor. We can read it not as that they took physical wealth, but that they took best elements of Egyptian culture and adopted and adapted them for Jewish use.
The Seder itself as an example is such an adaptation. The form of the Seder is the Greco-roman symposium, adopted and adapted for Jewish use, put to work in perpetuating our people's founding mythology.
“This continuous significance of the story is brought out with rare genius and consummate artistry in the actual structure of the Seder ceremony and of the Haggadah which constitutes its “book of words.” For neither is the product of a single age or environment—a mere heirloom or museum piece passed down intact and piously conserved. On the contrary, both are dynamic, not static creations—virtual kaleidoscopes of Jewish history—reflecting in their growth and development the various phases of Israel's career.”
The structure of the Seder is that of the Greco-roman symposium, and,
“When the door is opened “for Elijah,” we are plunged at once into the middle ages, for the real purpose of this act appears to have been to provide an effective rebuttal of the terrible blood libel which asserted that Jews employ the blood of Christian children in the preparation of the matzah. The door was flung open so that all might have a chance of beholding the complete innocence of the proceedings.
...The secular songs and ditties with which the service now concludes and which constitute its most recent—though most familiar—feature, take us straight into renaissance Europe. The famous ehad mi yodea (“who knows one?”), for example, has been traced by students of comparative literature to a popular and widespread “counting-out rhyme,” the earliest specimen of which appears in Germany in the 15th century. (in that earlier version, incidentally, the successive numbers refer to god, Moses, and Aaron, the three patriarchs, the four evangelists, and the five wounds of Jesus!) Similarly, the had gadya (“only one kid”) finds its earliest prototype in a 15th-century German folk song, der herr der schickt das jockli hinaus, though, here again, the wide popularity of the song is shown by the fact that early versions of it have turned up in most European countries.”
Judaism has changed as the millennia have passed, but its core values developed in a consistent direction. These values are part of the religion of Judaism, but there is more to Judaism than religion alone.
“The religion of a people was the regimen of its corporate existence, not merely a bundle of beliefs and of practices issuing from them. The reality of Jewish life lies not in Judaism but in the collective Jewish people. Judaism is merely an abstraction—the formulated quintessence of Jewish life—in precisely the same way that Hellenism is a mere abstraction of that which had reality and actuality in the Greek people.”
This affiliation with Judaism, one's "Jewishness," can find different expression for different people. For some, it lies with a literal interpretation the exodus and the Sinai story, with belief in god and in a literalist interpretation of the torah and subsequent halacha as god's will. For others, it lies with core values derived from the Jewish tradition and their Jewish heritage. While wider culture, language, theology, and even basic beliefs about the world differ between groups of Jews and Jewish individuals, there are core values Judaism that create touchstone's that all Jews have in common. These include respect for learning, seeking justice, and concern for and respect for one’s fellow (however differently that may be defined by different groups). While these ideals are not fully realized by all Jewish groups or Jewish individuals, they remain ideals. In the act of accepting or rejecting those ideals, they inform all who are influenced by their Jewish heritage. The chacham and the rasha are both informed by their heritage, are both shaped by it, and are both very similar, for all their difference in attitude and outcome.
 This essay was inspired by and quotes from: Gaster, T. (April, 1951). What Does the Seder Celebrate? Modern Commentary on a Traditional Festival. Commentary. Retrieved from https://www.commentarymagazine.com/articles/what-does-the-seder-celebratemodern-commentary-on-a-traditional-festival/
 Here I mean "myth" in the academic rather than the colloquial sense. A myth is a foundational story of a culture meant to impart lessons and inform people about their place in the world. it takes place in the past, but its primary purpose is to inform people about why the present world is as it is and how they are to live in that world.