Tbh, I think it's a bit of pick your battles. GOG and Steam are mostly good companies, but it's all closed source and I would bet money they are using AI to develop too. And they don't even provide any way that you could check that, because their code isn't open at all.

Is that really better than some open source dev developing with AI in broad daylight?

I totally understand why the Lutris dev shut down the discussion. The dev posted about struggling with mental health, and developing open source software is sadly really bad for your mental health. There's just too many people who think that the code is public and thus they get a say in it, even if they didn't contribute anything at all.

As an open source dev, you contribute without getting anything in return, and then you have to justify your actions in front of random strangers who often get quite aggressive. It's a really big problem in the FOSS sector. Look up e.g. the controversy around Marcel Bokhorst (M66B). He almost shut down all his great FOSS projects because of all the hassle he got from randos on the internet.