You're not getting much more power in an ATX build if you're only filling a 1080p display anyway.
Absolutely not correct.
Skullgirls, Guilty Gear XX Accent Core +R...
And also, most game-playing time worldwide is spent on games that are over ten years old and don't need a lot of power.
I don't think you're getting it. If that's what you want you can get a Steam Deck for $350 that does that, only it's portable and has a display and controllers...Same goes for a laptop. Or you could just buy an ATX that can also run more demanding games. This is not complicated. There are a plethora of better alternatives.