Depends how you want to want to measure it, 5 of the last 6 have been won by Mahomes or Brady. That counts as "usually" to me. Granted, that's a bit of a cherry picked window, so you could go with the last decade which would be 7 out of 10 which would also qualify. Then again, a few of those years were before Mahomes was even in the league. Since he was drafted in 2017, it would be 6 out of 8. During that stretch, Brady has won 3, Mahomes has won 3, and all other QBs combined have won 2.
So, yeah. The Superbowl is usually won by the team with either Mahomes or Brady.