Built a custom tower defense type clone for a client maybe 10 years ago… Coding it up in Objective C & Cocos2d was fairly straightforward. Probably spent 50% of the dev time taking in feedback, balancing the values on everything, progression of items, etc. what i’m saying is the functioning game logic (code) was really only one part of it.
I've built a few little games for myself both with and without AI, and completely agree. AI can help prototype an idea faster, or clone something very specific, but it can't make your control scheme feel good, invent a unique mechanic, etc (at least not yet).