Bethesda hasn’t made a great game since Skyrim.

Since Morrowind. Skyrim wasn't bad, don't get me wrong, but it can't hold a candle to its granddaddy in terms of world-building and stat-based character advancement, which was sacrificed for the sake of action combat that is not even close to good enough to carry the game.

But here's the thing... Bethesda hadn't made a great game before Morrowind either. That was their big breakout hit, and ever since then they've just been remaking that same game with slightly different coats of paint hoping to catch lightning in a bottle for a second time. They used to make more varied and innovative games before that, but none of them was really all that good. Terminator: Future Shock had fully 3D environments and enemies and a mouselook control scheme a year before Quake, but there's a good reason why the latter game is remembered as one of the foundational pillars of the genre and the Bethesda offering lies forgotten.

So I agree with you that expecting TES6 to be amazing is naive, but I don't think it's because Bethesda has gotten worse. It has simply regressed to the mean.

their ambition is getting the best of them

Always has been. I haven't played Starfield yet, but from what I've read about it online, including your description, it sounds a hell of a lot like a sci-fi version of Daggerfall, which was insanely overambitious for its time. It's a shame they seem to have focused on making the graphics prettier rather than the procedural generation more complex and interesting.