Here's my solution:

Solution #1:
Implement a mechanism which detects if a guy pings / quits* during the ongoing tourney match and, if so, fknock playing user who didn't ping / quit down the queue.
Match doesn't need to be counted in played match count, as that might result in rage-quit farming.

Plus: again, system which detects if player is playing when he pings. If so, don't let him rejoin and enter tourney (this quite often).

Solution #2:
Much like in other games, you get negative points counted for quitting. If you reach them within a day or 50 games or whatever, you get temporary ban.

I can't list in which game or game I saw this solution, probably in some flash multiplayer game I randomly played some longer time ago. ;'/

If ragequitter was dedicated, he'd make new alts to avoid this limit. For that, we could raise tourney minbelt to 30 or 50 so he has harder time getting there**

** which may result the player to put his superior skills to use vs low belt players in beginner rooms. Would raising tourney minbelt significantly make more
skilled players playing on beginner rooms to raise belt or TC? Not sure.

I'd think that 40% is too much, no need for that. But maybe like 20%. And they should raise the prize a little bit, like you said people ragequit :/

- Supported