Baldur's Gate 3 was in development for nearly six years even with asset reuse and basically being the only thing that Larian was working on. And that isn't even taking contractors into account (BG3 credits around 2300 workers).

I don't think you're making the point you think you are.

Many of the assets were reused from previous work (DOS 1/2). They did put in an insane amount of work over a very extended period, though.