This is a pretty tough ask really, hindsight being 20/20 and all. Fighters who have a standing legacy were almost always exceptional talents one way or another, not to mention incredibly driven to have actually persevered in the sport. It's so easy to nitpick at anyones resume, to say I think so and so wasn't as good as most other people seem to is kind of meaningless when I wasn't even breathing during their career, and have no idea what the perceived risk was for any number of their fights.
It's guys in the present who are overrated left right and center, but they are almost always exposed as such, killing any lasting reputation they could've had. Arthur Abraham was really overrated, now we know that, and noone will talk about him in ten years. Mijares and Hasagawa etc. were being regarded as great pound for pound talents, now the idea of them being mentioned in even good company is laughable. I guess a lot of it comes down to how much emphasis you put on achievement over ability, I can't think of one fighter who I really feel is overrated in both aspects Boxing is littered with supremely talented guys who couldn't apply themself the right way. Very few true overachievers come to mind. John Ruiz Sven Ottke Even those two clearly deserve respect for their dedication. I suppose if I had to name one great fighter I think is heralded a little to much, Id go with Julio Ceasar Chavez... But only because he was beatable and almost got to 100-0, not because he wasn't an incredible pressure fighter. The draw with Whittaker and screwing over Randall in the second fight sours his rep for me, but that's just my worthless opinion, he no doubt had a slew of very impressive wins.