My own theory POE2 is so freaking easy is that if you play it as big Open World World and start exploring you eventually will hit very much experience points and high level and then you go to end battle when very high level.
That's very much the reason. The game accomodates rushing through the crit story, so if you engage with not strictly required faction content, and side content you will quickly find yourself overleveled and overgeared even if scaling up is turned on. Deadly Deadfire mod addresses this problem but throttling experience gain, and increasing level scaling.
That said, end game content is decent - two optional end game dungeons have been patched to be more fitting for a max level party, and of course there are 3 DLCs which are a major spike in difficulty.
All that said, a lot of reputation of PoE2 easy difficulty comes from launch where game was very poorly balanced. Even professional reviews pointed out to unengagingly low difficulty, which is rare. Add to that custom AI editor, which means that one didn't even have to do anything in combat.
