Okay so basically the main problem is that Imas is a series where you are a male producer who works to produce idols. And Gakumas is a game about idols who are all high schoolers, and the protagonist is a college student. If you can put two and two together you can figure out what a lot of the problems are. But it doesn’t end there.
Every bad anisong Gacha trope is present in this game, so much that I can’t really even get into it because it would make this response too long. But it gets into a lot of really really REALLY problematic stuff (as much as I hate saying problematic because that feels like such a lame word, a better word to use is just, garbage), there’s siscon, incestbait, pedobait, transphobia, fat shaming, honestly homophobia if I’m being fully honest. Just overall it sucks bad and the writers behind the game are known for being garbage. It’s a shame cause outside of the writing I think it’s the most fun anisong game out there, but with the writing it’s… yeah. If you want to experience Gakumas without the bad stuff, read the spin-off Manga GOLD RUSH because it’s written by a different person than the game writers and it’s actually pretty good. I’m Probably not the best source to get into everything that I hate about Gakumas but if you have follow up questions feel free to ask.