I wouldn't put Boomer in the same boat as Randy. Randy's problems stemmed from motivation, or lack there of. Boomer had some inconsistencies and was shipped around due to a knee injury he suffered halfway through is career. He still made the pro-bowl six times after the injury, and made the pro-bowl on each team he went to, proving others gave up on him too early in his career. Without the knee injury, maybe the best ever...who knows. With that knee injury though, he was still a HOFer, amazing. Enigma solved...injury held him back.
With Deacon...I just flat out disagree with you. He missed 5 games out of 196 over 14 years. I think this points to Jones in the least attempting to squeeze out and leave every ounce of his talent onto the field. IMO his talent was fully fulfilled. The enigma might be his attitude and demeanor maybe, but he wasn't an enigma because of an unfulfilled talent, that's for damn sure.
I think a guy like "Bullet" Bob Hayes is a better example, and much closer to Moss in comparison to such a high level of unfulfilled talent. Hayes was world class athlete, and a Gold medal winner in the olympics. He might have been a better WR if he were able to lay off the "recreational" activities... *cough...cocaine...cough* I think Bob was also unmotivated over the long haul, but he definitely helped change the game and was a contributor to the way defenses cover WR's today.
All that said, you and Larry are correct. He was such a great talent that was definitely unfulfilled, and yes he was an enigma.