Yeah, Burns wasn't elite puncher. I just think that he'd fare a bit better on the indside. I would be more confident with more Sharkey footage available, for this era we have a lot from Burns and we know how he fought.
Burns was decent, and underrated for a very long time. I think the pendulum has gone a bit far the other way at this point though.
One thing is sure for me - Sharkey certainly fought in a tougher era. I don't see Burns winning a title in 1890s at any point. He didn't have right style to beat Corbett and Fitz/Jeffries were simply too good for him. He would be in a Sharkey/Ruhlin/Maher/Goddard tier for me, or maybe below that at Choynski/Slavin tier.
I think Sharkey is being sold short. While known as a face first brawler, in other fights, especially earlier ones like his first against Jeffries he fought on the back foot, dodging, slipping, countering and even dancing. I think he had poor punching technique, but it seems to have improved a lot, as he improved leaps and bounds before the rematch with Jeffries, presumably thanks to training with George Dixon I think if a good version of the Jeffries Sharkey II fight existed it'd do him a lot of favours. In the little that exists I don't think he looks nearly as crude as McVea.
I agree, he looks quite normal. It didn't help that he fought against much bigger opponent who was stronger man inside. McVea looks cruder than any other very good HW fighter I've seen on the film from that era. Edit: Outside of Firpo, he is the GOAT of crude brawlers.