A lot acually. Bert Cooper is one of them, can't think of anything else. Samuel Peter also a good one
Most recently it would be Gary Russell. Fights once a year since 2015 once he won a title (didn't even fight in 2021). This guy's going to look back at this time and moan, 'What was I thinking?' These were his prime money-making years and he squanders it. Man, I loved the days when Duran and Galindez would put the title on the line maybe 3 times a year and throw in 2 or 3 non-titles as well. To them, it was about making money and staying sharp.
Buster Douglas. Trained and focused, he'd have been the 5th elite of his era. He is remembered for the obvious. Had he kept that focus, he may have been also remembered for pulling off a second big upset and successfully defending against Holyfield, maybe even giving Lewis a rough time. I'd also say Bowe, but he ended up with CTE so fast, that may have been more of a limit on him than the buffet line.
Mando Ramos Jimmy Slattery Vernon Sollas Benny Lynch I know he won a world title but how great could DeJesus have been if he didn't go down the drugs route ? stay safe.
Teofilo Stevenson. He didn’t personally waste them but by virtue of him coming up in communist Cuba, his talents were wasted — although he did have incredible Olympic glory so not wasted in that sense. Just a great white swimming with minnows.
As @Mike Cannon also mentioned, Mando Ramos is a poster boy. Drug abuse effectively stunted a man whose potential was of a very high tier.