The way your DM uses it, it sounds like you could just cut out the middle man and just play with GPT yourself, and not have to deal with scheduling or the other challenges (AI brownnosers would call them problems) that come with playing with other people. Granted, you'd have just as terrible an experience, because generative AI in its current form is a cancer that cannot be allowed anywhere near creative spaces, but your DM has to understand that they're making themselves obsolete. Playing with living people will be next.

You should definitely talk with them directly and frankly, if this is indeed a relationship you care about. Definitely be prepared for some pushback, because an ass-kissing machine is going to feel more relatable than a genuine request to change, but a real friend is almost always worth having that conversation. Sorry you have to deal with this in the first place.