Firpo is being called a puncher here, and he could hit hard, but he really wasnt a one punch guy that could just turn a fight around on a dime with his power. Every fight we have of him where he scores a KO it was done by a very physical, mauling style and then when he had the guy vulnerable, repeatedly clubbing him. There isnt anything wrong with that per se. Those guys have a place in the argument as well but I dont know that Firpo is going to get behind on points to a guy as big as him and then just bring the fight home with his punching power. If he doesnt have the size advantage that he had in the 1920s hes going to be hard pressed to use that mauling to wear down these big guys to the point he can start pounding on them.
Definitely the Hasim Rahman of his day. Tuff and crude. But a haymaker could still take out a champion of the first rate like what happened to Lewis.
The youth and pace of even raw heavyweights of those days would be a factor today. Also the matching of modern prospects is a lot more one sided.. you can get a whole lot further with a pretty record without facing anyone decent than you could then. That stuff goes a long way when it comes down to swapping punches for real.
I honestly don't think he would make the top 50 He is just horrible on film, perhaps the worst heavy title challenger, skill-wise, ever filmed.