Sure but Ferrer wouldn't be favored over Coria either. Coria is a much better clay courter than Ferrer. So for Gaudio (who was a huge underdog) to beat Coria was still a huge win.
I agree that Gaudio's slam record is "better" than Ferrer's. His 1 slam title > Ferrer's SFs/QFs/1 slam final. But like Gaudio, Ferrer made the final of Roland Garros. What made the difference between Gaudio
"reaching the pinnacle" and Ferrer
"never doing so" is that Ferrer faced arguably the greatest clay court player ever (who was 7-0 in FO finals); Gaudio faced Guillermo Coria (who was playing in his first slam final, and with the added pressure of being the huge favorite).
Regardless, the thread asks who had the better career, and IMO 1 slam title does not make the better career. All Gaudio has over Ferrer is a lone slam title, so only those who think slam wins are everything would say Gaudio had the better career.