I would regard them with extreme caution. If you do rate them however, the smaller guys come surprisingly well out of it.
I don't really buy this. Absolutely nobody in or out of the ring considered this at the time. The one thing that nobody seems to have questioned about Marciano, is his power.
What, Walcott's last fight where he laid down? Marciano put a hurting on Walcott over 13 rounds in the first one. It wasn't just a one punch KO. Joe was obviously at the end of the line. He certainly didn't want to repeat that kind of punishment. He got buzzed, went down and saw no reason to get up. He was already retired.
Look at the combinations that Louis had to throw at Walcott to put him away, then look at the way Marciano scrambled his brains with a single punch.
Looking at the various tests over the years, it appears that they might not be measuring force in exactly the same way.
Watch that fight again. Walcott is gassed. Marciano is landing on him well for the last 4 or 5 rounds. Walcott does have one excellent round in there (11?) but the rest if Marciano softening up Joe. The final shot is an exclamation on a sustained beatdown, certainly not a one-shot KO.
By that logic you can argue that any fight that goes into the late rounds represents a softening up process. While Marciano was getting some good shots in, its not like he had been stuffing Walcott over the course of the fight. He was behind on the score cards, and had landed less than he did against a few other fighters. The end was delivered by a single well timed right hand, while Louis had to throw every combination in the book at Walcott. I would add that outside of the Louis fight, Walcotts last knockout loss had been 14 years ago when he was a semi professional fighter.
Marciano was nailing him in the latter rounds. In fact, the most famous photo from that fight, a right landing flush on Joe and distorting his face grotesquely, tho often reported as the final right hand of the fight did in fact occur a few rounds earlier. I would add that at 38 years of age, guys "get old overnight". There is a reason that Walcott essentially retired that night.