Hamlet
Yea...... winning is not a punishable offence I'm afraid.
Besides, if he's significantly higher level manager his XP and research power will be minimum and sooner rather than later his overall XP will deteriorate as well. There really isn't any advantage for anyone to jump into a league of much lower managers just to accumulate W's. Talk about filling himself up with a dose of lethal false sense of security.
On the other hand, having such significant higher level manager has the opposite effect on lower level managers. You want to have as many level 20's as possible.... that's a sign of a successful and attractively competitive league.
I take it said manager has left your league. I didn't see anyone in your league that fit your post.
It's the Diego guy. He keeps winning literally every single race. Can you do anything, like reduce his level, car points, etc?