High rev rate means there are more revs to pick up and deposit oil.
A thumb bowler using urethane at spares will not cause carry down.
Even a high rev thumb bowler usually has an altered release for spare shots.
It's the no thumb bowlers shooting at spares. Plastic, Urethane, even a reactive ball that doesn't flare doesn't matter.
I've done the experiment myself. 1 game no thumb spare shooting. Then try bowling a normal game and terrible carry down. But bowl 1 game practice spares with my thumb and no problem with strike shot.
Everyone is creating some carrydown with spare shooting, but usually it's just too little, and being wiped away by all the strike shots to be of any noticable consequence.