I can assure you ice does not have a problem with sableye, this is coming from an ice user. Frost Breath Walrein and Lapras do a great job of getting through the CM boosts, and usually 2ko if physically defensive. If it's specially defensive, strong physical attackers such as Mamoswine or (in rarer cases) Mega Glalie also make a quick and easy clean up.Reason to ban: Mega Sableye is annoying, and very hard to beat with certain types.
Reason to leave: The ban arguments can be applied to literally any strong mega.
The types that suffer the most from Mega Sableye are ice and electric, which don't utilize much usage anyway and are outclassed by almost every other type.