You are definitely being biased against Manny and not putting into context when the wins occurred. Manny's top wins:
JMM: Not the blown up lightweight that Floyd beat at 147, Manny fought the prime counter puncher at a weight that suited both. He fought him multiple times in JMM prime, while he was rated P4P. JMM is a HOFer easy.
Barrera: Coming off of a dominating win of Hamed and close win over Morales, he was P4P top 5 and a HUGE favorite to win. Pac destroyed him during his peak and at his best weight. HOFer.
Morales: P4P ranked when they fought the first time, Manny lost a close decision but came back to destroy him twice. Another HOF fighter Pac fought during his prime.
Cotto: One loss to Margo, a much bigger man and still viewed as in his prime and dangerous. This is a very underrated win, especially considering how Pac stopped him. HOFer.
Bradley: Ranked P4P #3 at the time and undefeated. Manny beat him twice (don't care what the judges said) during Bradley's prime.
Hatton: lesser version than the one Floyd beat, but one look at that fight n u can see it wouldn't have mattered. Manny destroys Hatton any time they fight like that.