Yes, it is. On average ofc, but that goes without saying. If you are an average player in a poker tournament in a field of 100 players, you win that tournament 5 times more often on average than in a field of 500 players. This shouldn't be difficult to understand at all. Obviously there are some other factors as well, like if the UFC had a known tendency to sign better HW talent on average than LW talent, but that would be really difficult to prove, and it can also be the opposite.
In reality the skill level at HW might be even worse than that, if the theory of other sports stealing the best talent especially when talking about HW sized athletes, holds any weight.
If I wanted to be intellectually dishonest like you, I could just say lets compare their skill level with an eye test. HW's would look really terrible in that comparison, but because I know its impossible for a HW sized fighters move like LW's, I'm not arguing that. You have to learn how to be objective, reality doesn't care about your feelings on Stipe. LW is a lot more competitive than HW, why willingly make yourself look stupid trying to argue on that, just to make Stipe look better, I will never understand that kind of stupidity. Don't bother answering, because I won't read it. You are just incapable of being objective.