Wasn't necessarily saying he was a candidate, more pointing out that the strength and beating up of whoever the other guys were going on about is a little redundant when we throw someone like him in the ring. Then again, if we are talking greats, the guy had an incredible career that spanned a hell of a long time. In his arena, he stood up to a lot of great names and he defended his belt something like nine (too lazy to fact check...) times.
When magazines and commentators ask this question, they always look at dominance during their period and without doubt, GSP dominated.
No doubt he was great in his time, he changed the sport single handedly. His conditioning and skill set in the ring, was unmatched. I'll miss GSP, but the sport grows in leaps and bounds because of him.