Is there a cap to MMR and rating?

That’s a really strange way of saying
BGB: 21.12 lobbies per character
RSS: approx 9 lobbies per character.

But also you’re kinda proving my point. Blitz is actually picking up steam as people get higher. Because people want to push Blitz for novelty reasons. In each bracket range as you described, Blitz players are playing more lobbies than Shuffle lobbies and, as you go higher, the difference is more pronounced. Shuffle just doesn’t have the retention. It is what it is. People no press Q, number no go up