I don't know anyone who has gotten banned for gamerscore mods. I just know of it getting reset. I went from just over 300k to 0. I also can't get those achievements again if I wanted to. It's almost like the system thinks I have it unlocked, but I don't.
I modded my gamerscore in 2013 - 2014, and it ended up getting reset in like 2019. I have friends who modded, and to this day are getting their gamerscore reset. It is weird, but apparently they do still care.