Why is it such a given that bullies are dumb?
In both middle school and high school, I was bullied incessantly by kids who were doing just fine, academically. Some of them went on to be quite successful people. Bullies nonetheless.
It would be so convenient (and karmically just) if all the awful kids went on to be dropouts and losers in life, but sometimes it doesn’t work out that way. Sometimes they’re smart kids, but they’re just assholes.