Im not big on Marciano actually, but, when anyone asks why Sharkey was still there after 25rds, Jeffries lovers pipe up oh, Jeff had an injury,otherwise he would have taken Sharkey out. Well he didn't have an injury in their first fight and Sharkey was still there after 20 rds that night, a faded Corbett was still there into the 23rd,and a late 30s Fitz into the 11th, So lets just admit Jefffries was NOT A HUGE BANGER, END OF STORY.
Therein lies the problem. I wont say one way or the other whether an injury free Jeffries KOs Sharkey. But, a failure of an opponent to finish off a Great (arguably all time great) fighter does not equate to a lack of ability to hit. All of the very best bangers struggled from time to time to put away lesser fighters, whether they be top quality or otherwise. Jeffries was no different. He took his time with some great fighters and he finished others off quickly. I dont think he had a tyson or Foreman level type punch, but he was still a big banger in the scheme of things, and certainly in the top tier, imo.
You are wrong on the weight issues but it's hard to verify as reported weightgs varied wildly back in Sharkey's day ...
By all accounts Sharkey fought a much more safety first fight in his first encounter with Jeffries and was far less agresive. It should also be taken into account that Jeffries was stepping up in competition for ther first time.
It should also be pointed out that Jeffries had allready had 2 ,20rd bouts when he fought Sharkey. I dont doubt the big guy could hit ,I just don't see him in the Liston ,Louis,Foreman league.