Dempsey was rusty and sparring is one thing a real fight another.Jack Delaney watched their spar and said," Harry looked good ,he made Jack look slow in there,but over 10 rds he would get clobbered nobodies doing that to Jack for a whole fight ."
By using your brain. There's heaps of footage of fighters Greb actually beat and there's also any amount of documented resume. Put a little effort in.
My understanding of Greb is that his unique style , his speed, stamina and chin made him a nasty challenge for middleweights to heavyweights in his day .. the Dempsey sparing prior to the Miske fight seemed to even up as the days progressed with a less surprised Dempsey making the short but furious sessions more competitive than the initial .. how those two pan out in a distance fight with a prepared , top conditioned Dempsey who knows but I'd lean towards Jack with a vicious body attack taking it's toll .. as far as Louis , I feel a prepared Louis could do at least what a prepared Tunney did which from my understanding was use reach, speed and strength to punish Greb to the body ... the key is prepared because who knows how any initial encounter would play out .. Without film we all speculate but there is a ton of written descriptions and bizarre photos that indicate what a speed freak spoiler type Greb could be ... he's an enigma ...
Definitely problematic factoring the dynamic and respective successes in sparring sessions in order to formulate a likely complexion and outcome in a real fight. Even Carpentier had his brief moment in the sun during his actual fight with Dempsey (sub that for a brief success whilst sparring in a gym) but then Georges was settled up well and truly before the completion of 4 rounds. Smaller, clever opposition have a habit (naturally) of having some shining moments against their bigger opponents but ultimately, when the bigger man is no slouch in the skill dept. himself, the smaller man doesn’t often win the day.