He did beat the #1 Fly in the World at the time. IMO the Tachi Belt was as good as it got for Flys before UFC. So I consider the UFC Champ to be the legit champ.
The problem I run into is I personally felt McCall won the 1st fight vs Johnson. He clearly lost the rematch though. So beating Creepy on the way to the belt makes him legit in my book.
You can consider him a true champion if you want, i cant though....not when looking at all the other champions.