Barrera didn't just beat Hamed, he totally outclassed him. Canelo did not dominate GGG in any fights, arguably lost the first one. So yes, Barrera's feat is much more impressive.
He's De La Hoya level not Manny/Floyd level. He's 17-3 for title fights which is atg level. He's only lost to elite guys like Mayweather, GGG, and Lara. Four weight champion. The problems are that all of his best wins were robberies, the Kovalev fight looked fixed, the best fighter he's beaten is Danny Jacobs, and he tested positive for steroids.
Had he beaten Golovkin the two times they faced it would have been a lot closer. Golovkin was robbed.
Would need another several years of continuing to beat #1, top 5, and top 10 ranked opponents. Floyd beat something like 26 of them. So, yeah.
Marquez is one of those dudes that aren't KOable. But Pac came really close. You saw Floyd put a beating on Canelo, right? If he stepped on the gas, he would have had a good shot of doing so. Marquez is also more skilled than Canelo. Marquez is the worst possible stylistic matchup for Pac. Pac would tee off on lead feet Canelo.