Who knows, primo wasn’t really taught how to punch properly like Wlad. If they had the same trainer maybe he hits even harder.
In terms of what was actually demonstrated I’ll say Klitschko. Knocked out a lot of big men with crisp power shots and some were fairly durable
Are you sure about that? If you're just going by size, they were the same height with Wlad in the 240-250 range and a not as cut Preem in the 250-270 range. Though he very rarely went for max, I've heard some impressive numbers put up by Wlad. Preem claimed a 300 pound clean and jerk if memory serves. That is less than, for instance, great triple jumper Jonathan Edwards, a guy who at 160 could put up 350 lbs.
Maybe strength alone would be close. Hitting power however is speed plus strength and properly applied weight. Carnera had only the strength. He had weight but couldn’t properly apply it and no speed. So not much power. This is a no contest Wald by a really wide margin.
Carnera but he didn't use it nearly as often. He'd likely win if you had them hit a bag as hard as they possibly could. But in the sport of boxing Wlads power was more "relevant".