I have a consumer app that swaps between the 5 bigs and wholeheartedly agree, except, God help you if you're doing Gemini. I somewhat regret hacking it into the same concepts as everyone else.
I should have built stronger separation boundaries with more general abstractions. It works fine, I haven't had any critical bugs / mistakes, but it's really nasty once you get to the actual JSON you'll send.
Google's was 100% designed by a committee of people who had never seen anyone else's API, and if they had, they would have dismissed it via NIH. (disclaimer: ex-Googler, no direct knowledge)