I agree, if the topspin has some pace
I agree that if you have flat to just needed spin on your shots then you can have an advantage over overworked spin players IF you get your timing used to their ball early in a match and all else is equal (movement, respective technique level, etc). One of 2 things happen:
1. you get your ball deep and they have to pick up on the rise, which is harder to do with a more vertical spin path and not end up with a defensive or short shot
2. your ball goes into their sweetspot / wheelhouse but because your pace is flatter they have to accelerate their racquet fast to get the loopy shot. if you can get the opponent running their capacity to do this consistently is diminished and eventually you get a weak ball you can flatten out for an approach or winner.
I think what throws a flat to mild spin player off more is a lack of rhythm that may result from a non-consistent, often non-pace shot, not necessarily a heavy top spin hitter that is consistent and provides some pace once the ball bounces off the ground.