Is Louis's 25 title defenses the greatest accomplishment in boxing?

My exact quote was "went from being belt holder at flyweight to beat the crap out of a future MW belt holder". That is of course literally correct, but I do see your point. So to make it both literally correct as well as in essence: Pac won and defended a belt at flyweight and went on to win a belt at JMW with a one-sided beat down.

Any way you cut it, Pac went on to beat guys who weighed about 50 lbs more than he himself did when he won his first belt. And in Cotto, he actually outclassed and beat up a quality fighter that weighed probably about 40 lbs more than Pac did when he won his first belt and about 15 lbs more on the night.

For me, that is one hell of an achievement.

 

It really is a fantastic achievement. Definitely worth a mention among the great ones.