Then some should rethink their list: Dempsey or Marciano punching harder than Tua, Tyson or Lewis. :nut
Marciano at least knock a good number of his foes out cold. Were Tyson and Lewis didnt do it as often. Sure they had the flash knockouts, were after the ten count, they were ok, but it took a while for the 2nds to bring around Walcott or Layne.
...great question! But as the list provided is all heavyweights you'd have to think not. There have certainly been some insanely hard punchers in lower divisions - look at the list of Mex bantams, and PacMan, just as examples.
If Tyson is there Lennox Lewis should be somewhere above him - he blasted out all their common oppenents in quicker [with the exception of Bruno, who he stopped a better version of anyway]