Personally, I think he would have. Holmes was simultaneously one of the most dominant and one of the most vulnerable atgs. He didn't really compete in a great era, and he won A LOT of close fights. Under different refs, judges, or rules ( I.e. a 12 round fight instead of 15, or a red waiving off a fight after a heavy KD, or some of the close scoring going against him) or a few other tweaks to competitive fights, he could have lost over a quarter of the title fights he won. That's unusually high for an ATG. Historically, he was also atypical for a great champ, in that he was only somewhat larger and harder hitting than average. Most HW champs have either been substantially larger or more powerful than average, or both. Stevenson would have been both. Backed by the best amateur legacy in hw history. Hard to count Holmes out, but I think there's little question that Stevenson would have been the dominant hw in that era if he'd turned pro.
If Soviet and Cuban amateur talent were allowed to go pro... The last 30-40 years of boxing would probably be very different.
Taking nothing away from Teofilo but Holmes would have schooled Stevenson. BIG difference between AMs and PROs...
That'd have sent shockwaves that would affect today in a big way. Much of that Soviet and Cuban talent still has to come through U.S. or German promotion because that's where the infrastructure is, and those fighters aren't the first choice of what promoters or networks really want. The Russians today are finally taking steps and putting on big shows, but the scene is still underdeveloped enough that a world-level talent like Lebedev had to retire for a few years because the opportunity wasn't there. World-caliber amateur fighters still go unsigned or unpursued by major promoters (which is one reason the AIBA can always have a steady supply of talent for the WSB). Picture the coaching and promotional scene today if those fighters had access to quality professional support and that infrastructure had been in place for decades. Makes you wonder what we've missed out on, not only with the obvious guys like Stevenson, but the ones nobody expected anything from who turned out to be something special.
Stevenson was the prototype of the modern heavyweight, he literally reminds me of Lennox Lewis in many of his fights. 20ft jab followed by a wrathful right hand no one seems to escape. Looked unbeatable. BUT... 15 round fights, experienced, iron chinned, scrappy fighters that fight nothing like the ams, and worst of all, the hard partying American lifestyle, which seems to curse Cubans to this day, would really put even the greatest fighters to the test.