As for the consensus, yes. I think this is generally the case that most believe that the Exodus was almost entirely fabricated on the basis of oral tradition. Personally, I’m disinclined from saying it was made up entirely whole cloth. The reason for this sets up the reasons for why I think it was written in the first place.

As you’re already aware, the Exodus narrative is central—and has been central—to Israelite and Jewish identity. In the early stages of state formation, hopeful leaders need narratives they can use to rally support as they approach national identity. (E.g., as stupid as it was, “And who has a better story than Bran” would have worked at the beginning of rallying public support for the creation of Westeros—similar to how Aegon the Conqueror did, but I guess D&D kind of forgot how such things work. But I digress.)

So, why was it written? Ultimately it’s a difficult question to answer, as any honest archaeological work will tell you there’s no proof for the event and so reconstructing such history is nearly impossible beyond being conjectural. So, my theory: there were traditional social memories of some kind of relationship between Egypt and what would become Israel. This shouldn’t be surprising, because we do have record of Egyptian involvement in the Levant thanks to the Merneptah Stela (usually cited as 1204 BCE) and the Tale of Wenamun. Merneptah is difficult because we don’t quite fully understand the determinative used with the name Israel. It means “people group,” but it appears in a larger list of cities destroyed by Pharaoh Merneptah. ¯\_(ツ)_/¯ It’s possible there was a very small, Proto-Israelite presence in Egypt at some point that would have served as the source of such memories, but we can’t be too certain. These memories were obviously derivative of multiple sources (hence the presence of what we call doublets—two slightly different accounts of the same story; e.g., did Moses receive the Law at Sinai or Horeb? Was his father in law’s name Jethro, Ruel, or Hobab?). These traditions were eventually put into writing, expanded, edited, and redacted to eventually come into their final form as we have it (read: them, there’s no singular source for us for these texts). These exodus traditions were used as a form of social identity construction—an integral part of state formation and preservation. The use of national literature would become far more important in later periods—especially for the Deuteronomist, who loved to use the Exodus as a central theme for explaining his perspective throughout the Deuteronomistic History (Joshua, Judges, Samuel, Kings).

I don’t think it’s necessarily commentary on Israel’s relationship with Egypt as Egypt kind of falls off pretty significantly after the Iron I. I think it’s national literature, intended to construct social identity by constructing a literary Other. The othering process creates an in/out relationship that early Israelites could identify with—especially in light of the nearby Philistine threat during the Iron I–IIA, eventual Assyrian involvement in the southern Levant in the Iron IIB and later, Babylonian incursions and deportations in the 6th c. BCE, etc.

A couple of sources that might help:

I. Finkelstein, The Bible Unearthed — he’s a little over the top with the low chronology, but deals with a lot of important stuff in a very accessible way.

W. Propp’s Exodus commentary is top notch in the Anchor Bible series.

E: fixed a couple of typos.