Who is the boxer you thought had the potential to become "The BEST Ever".... but didn't?

Ike Williams
Langford
Ezz Charles
Duran
RJJ

 

I think the parameters you describe are unrealistic — someone would really have to be a complete and total flop/fraud or either die very young before reaching potential to be on course to be the ‘best ever’ and not win a world title (especially in the more modern era of a belt to be had on every street corner).

That being said, I’ll try to keep it at least closer to your original intent of guys who didn’t win titles or didn’t quite cut it who looked like they might at least in a brief, shining moment:

* Nino LaRocca was a Northwest African-born Italian with marvelous reflexes and speed who beat a number of prospects, suspects and quite a few outright contenders before he lost a fight on a cut (no big deal) and then got decapitated by Donald Curry. He still notched a few meaningful wins after that but was more or less washed at the world level after being dispatched in his title shot.

* James Scott beat top-ranked Eddie Mustafa Muhammad and Yaqui Lopez, who was in the top two or three, in dominant fashion fighting behind bars in Rahway, NJ, but when the WBA ruled that it would not enforce him as a mandatory and force a champion to go into prison to fight him and NJ officials decided not to grant a furlough for him to fight in Atlantic City to get a title shot, he lost some steam and was beaten by Jerry Martin and Dwight Qawi. He was the absolute real deal but circumstances were such that we never found out if he could best Matthew Saad Muhammad or repeat his win over Eddie Mustafa.

* Tony Ayala was another one who might have been in this category had not his being a brutal, violent ****** (along with drug and alcohol problems) derailed his rise. Came from a fighting family, seemed to be the best of that lot but his damage was self-inflicted.

* Lemuel Steeples was thought to be the best prospect of the U.S. amateur team that died on a plane crash on the way to a competition in Poland in 1980. (Bobby Czyz iirc missed the plane.) No telling what he could have accomplished but he beat Milton McCrory and some other future contenders in the amateurs, although he lost a couple times to Ronnie Shields and to Donald Curry.

 

Of course there’s Teofilo Stevenson and Felix Savon and a host of Soviet bloc amateurs who never turned pro who showed in the amateurs that they could compete with and beat fighters who would become top pros (including future world champs), but amateur is different than pro so who knows —- at the very least, they’d have been top-tier prospects if not for politics keeping them out of the pro ranks.

 

Had Roy Jones retired after the Ruiz fight, or at least the first Tarver fight, he would be in the conversation.

As someone who doesn't penalize bad career management, for going on too long, I still put him up there when considering his FOURTEEN YEAR professional career.

 

Easily Roy Jones.
Watching his fights back in the mid to late 90s you got the sense you were seeing something truly special. If he would have quit while he was ahead - and not gone on for all those years post prime he could have ended with a career record more befitting of his talents.

 

Never thought he'd be the best ever but Jamie Garza was 25 years old was the super bantamweight champ and was 40 -0 virtually all Ko's.
Then he got reckless after dropping Meza and ran into a left hook that ko'ed his career, as he never really recovered. After his 40 -0 run he went 8 wins 6 losses and retired .But when he was right Garza could sure get a guy outta there

 

In my time there was a sparkle in the eye for Fury… he dethroned Klitschko in an ugly unsatisfactory way and abandoned boxing for 3 years… okay… lot of unanswered questions especially one named Cunningham
… then he returns goes 2-0 against guys he should beat, jumps in with Wilder “Draw” but really we saw enough let’s move on? 2-0 again goes to war with Wilder okay fair needed to happen… but not the unnecessary rubber match, that essentially left him spending himself on a trilogy that while entertaining and profitable took a lot shall we move on? Beats Whyte and to me that’s a good opponent right after Wilder 3, back on track? then Chisora for the most shameful trilogy at HW… then there’s the MMA fighter who debatably won in there debut, yep, right he had no depth of character he trained not a single round and brought the GREATEST shame on the sport (inside the ring) of any HW champion ever - Valiant losses to Usyk x2 and we are sort of left with a 36 year old guy who belonged to another era but went boozing in his prime only to was up on new shores totally disinterested AGAIN… what’s left for a legacy now? He’s possibly number 2 of one era when he could’ve been number 1 for two if he’d just trained like a professional.