I've been working on a client/server game in Unity the past few years and the LLM constantly forgets to update parts of the UI when I have it make changes. The codebase isn't even particularly large, maybe around 150k LOC in total.

A single complex change (defined as 'touching many parts') can take Claude code a couple hours to do. I could probably do it in a couple hours, but I can have Claude do it (while I steer it) while I also think about other things.

My current guess is that LLMs are really good at web code because its seen a shitload of it. My experience with it in arenas where there's less open source code has been less magical.

I suspect you are not using plan mode?