What do you tell a friend who's convinced he can make his own ttrpg in < 3 months

I imagine this situation is probably pretty common. I have a friend who has decided to make his own ttrpg. He wants to make his own ttrpg because he gets annoyed by things DND does, but he has only played a few other ttrpgs (DND, Call of Cthulhu, Pathfinder, and Dune I believe). He wrote 30+ pages of his "system" and I can only describe it as...DND but homebrewed to be horribly unbalanced. He hasn't playtested anything yet, but just skimming through it it's pretty clear that it's not playable. He was already happy with it after only a month of working on it though. I suggested that he try other ttrpgs first because what he made felt way too close to DND but he got very offended by that suggestion. He's already asked another friend to make art for it and he's convinced that he can get it published and make money off of it...

There's probably no talking him out of it, but maybe I can send him some things that could help. From what I read/heard from him, it sounds like he wants to make an universal ttrpg that's customizable (custom spells, abilities, training in different skills, etc.). I don't want to utterly destroy his dreams, even though most of us are convinced that he will never publish/make something playable.