I would say it's very possible to tell. Wlad was the naturally bigger, stronger, faster, more athletic and more well schooled fighter, with multiple legit one punch knockouts on video, so it stands to reason he'd be the harder puncher. Sometimes things aren't as complicated as we like to make them, and this is one of those times.
No sorry. I should have been more precise with my wording. I meant which CWs hit harder than the current top punching HWs.
Wladimir. Let's not forget that apart from the size difference etc, that Wlad is essentially a boxer, and a cautious one at that. He doesn't commit 100% to his shots like Shavers. He's a guy who is very happy to peck away and win a points decision over a guy that he could have KO'd had he taken 1% more risk and opened up a little more against. Despite that, he still has a ridiculous KO percentage over top shelf opposition. When Wlad sits down on his punches he rocks people's worlds. He blasted Mercer off his feet. Stopped Brewster. Had giant iron chin Wach reeling all over the ring. And the artillery shell he hit Pulev with ruined his career, he's not been the same since. It's not that complicated.
Ask my old buddy Randall Tex Cobb how hard Earnie punched . He said every shot shook him from head to toe Earnie was the only man to ever do that
Steward also said Lewis was the hardest puncher and most talented boxer he had ever seen, let alone trained. Also at one point said Maurice Harris was the most talented HW he ever worked with. He generally said whatever he needed to placate the fighter he was employed by so I take his evaluations with a grain of salt.
Maurice Harris was an interesting character... Lewis' main sparring partner for several years, and I recall a couple of other trainers saying he had unbelievable talent in the gym. Just couldn't consistently bring it all out on fight night, he had some mental weakness and chin issues for sure too.
Making a weight argument here is sort of irrelevant. If a born puncher is around 210 pounds or so they can KO anybody. Kudryashov landing a left hook flush on any current HWs chin they would probably go night night. Wlad has 30+ pounds on Mike Tyson but Tyson was the bigger puncher. Valuev was the biggest HW champ in history but he was featherfisted.
He had some talent but it's still a ridiculous statement and Steward made too many of those for the guys he trained for opinion to be taken as gospel imo.