In the context of prize fighting, fraud means his fights were fixed ... quite a different thing than saying someone is overrated. Are you sure that's what you mean to say?
In terms of overrated, GSP being overrated means he shouldn't have been rated the number one WW, which raises the question who should have been rated number one while he was UFC champ. Some people say it should have been Askren, and I've heard people say Nick Diaz should have been rated higher than GSP even while GSP was champ (can't say I ever followed the logic, but it was said) ... and some folks were saying that Hendricks should have been rated higher than GSP even before they fought (ie GSP shouldn't have been fighting Condit or Diaz).
Personally, I'd argue that GSP was properly rated the top WW while he was UFC champ - its inherent in being the champ. But ratings are subjective, so its logically possible that he should only have been rated 2nd or 10th or even 1000th, depending upon the subjective criteria used. I fully expect to hear that saying that is huge bias against GSP, but its inherent in subjectivity.
If its about overall favorite fighters, I'd pick Fedor, Jones and Anderson above him, though he's in their league and its subjective. And Jones testing positive twice is pretty bad - it likely means he was using extremely high doses (the difference between going 5 mph over the speed limit and not getting caught and going 50 mph over the speed limit and getting caught).
The reason I say favorite and not GOAT is because its impossible to meaningfully compare dominant champs in different weight divisions. Anyone who can actually do that kind of analysis is making too much money betting on real fights to bother getting into the argument, since its an order of magnitude easier to predict the outcome of two fighters in the same weight division than to predict what would happen if two different weight fighters were suddenly the same size (ie P4P all time great).