If you think DOOM and CS aren't brain rot, you might be just falling into nostalgia. Shooting demons and other players and spraying bloody gibs is absolute brain rot.

I play Roblox with my 9 year old, and no, they're not anymore brain rot than DOOM or Quake deathmatches were. Capture the flag or tower defense was almost never the point. It was being first in a deathmatch.

Quite frankly today's Roblox games tend to be a lot more enlightening, innovative and entertaining. Not all of course but many.