From the write ups he seemed to be able to do whatever you so pleased. Primarily a boxer puncher, capable of fighting at any range with a frightening natural instinct. Even late into retirement and drunken obesity, he was able to confound and toy with Tom Sharkey, a top contender of the time and debatably a heavyweight champion.
One contemporary observer described him as being "as clever as any man." Terry McGovern was sometimes compared to him stylistically.
Where was this coverage ? I read Sharkey handled him w kid gloves and Sullivan admitted it himself ..
My sense of the man's style is that he had more skill than many give him credit for but less than some give him credit for. These are educated guesses based on what people in his time said about him, since there's no film of any of his fights available. Some things are certain. In his prime he was much better than his contemporaries, and ahead of his time. Many knowledgeable boxing people in his era were astonished by what he could do in the ring. He was looked upon with awe by many of his peers. We have to consider all that when trying to evaluate him as a fighter. He was the best around for many years, IMHO, of course, and yes, I think he would have beaten Godfrey and Jackson had he fought them at his best. And it's a shame that he didn't.
He was supposedly very fast and agile on top of packing elite power, relying on those attributes in his style. Contemporaries lauded the level of his skill but then what did his contemporaries witness to compare him to?