The Sharkey of the mid to late 1920's was a hell of a fighter .. he also took a terrific shot .. I think Jack beats him easily ..
Shavers would be a live underdog, his power was serious but do you really think he would beat prime, focused Sharkey?
I know you usually going for the modern, good logic too. But Shavers wasn't really modern and Sharkey was good, really good, ahead of his time. This fight is a 1950's fight, they meet halfway and Jack outboxes Earnie all the way, edge of the seat stuff, just too smart.
Sharkey looks good at times in contrast to the level of fighter and athlete he faced. When he faced true elites, Dempsey (who was past prime) and Louis, he was ultimately blasted. I am more impressed with, say, Quarry than Sharkey. Quarry actually had to face athletes who could box and/or punch. I think Shavers has a very good chance to catch him. I think the Shavers who faced Ali could do so early or late.
You think? Jack stayed in the box with Jack and outboxed him. (Did I write that?) And I can't believe that a good poster like you mentions the Louis fight, that was just money for fish bait. Sharkey had a better outside game than Quarry, equally good at mid range, smarter, but Quarry was stronger. BTW he beat Shavers easy. Jack would be different, angles, slides, rapid punches, readjustments, fast jab. No doubt, Shavers could nail him but Sharkey took a good punch and believe it or not, Earnie didn't always finish.