The main factor with the rating of Gonzalez in regard to Rosewall, is how much weight you put on the head to head World Series. Gonzalez became after his rough baptism on the first Kramer tour in1950, a kind of specialist for this format. His legendary status was primarily built on his big series win over Trabert, Rosewall and Hoad. He had however some factors going in his favor: Much more experience with format and surface, a psychological advantage of the old pro over the new pro etc. McCauley describes the Gonzalez-Trabert series of 1956 as the first really big event on the pro tour. Gonzalez won it with a one-sided score, but almost all matches were played indoors, which favored Gonzalez' serve, and denigrated Trabert's strenghts on hard court (where he grew up in Cincinnati) and clay (where he was probably the best in the 50s). I personally find Gonzalez big wins in the round robins against very tough opposition, at Forest Hills and LA in 1957 and 1958 more impressive than his World Series wins over new pros.
I also think, that Gonzalez takes both advantage and disadvantage from the fact, that virtually very few, if any living people saw him playing in his prime, and not much of his game is transported on (longer) videos. This had negative impact, because his memory is hurt by the media situation (see the Tennis Channle ranking). It has however an advantage, because his status grew in oral memory by contemporaries to mythical heights. That he had a great, maybe the greatest serve ever, no doubt, but what about his backhand, which was only sliced? In the 50s, Trabert or Hoad already could hit drives from the backhand. What about his forehand (in comparison to Kramer or Hoad), which was his major weapon hin his early career, but became somewhat inconsistent in his later career (according to sources like Rosewall)? His volley style seemed to be more a touch game (according to the videos i have see from his Pasarell match in 1969). It think, all this makes the evaluation of Gonzalez' game, and the separation of reality and myth quite tough.