I have more sympathy for your argument that Corbett was not as good as history implies, than your argument that he was overrated in terms of his boxing talent. Surely the primary reason for the former is that he was boxing rings round everybody, whether he won or lost.
I would think Ali looked decidedly underwhelming and that's exactly what I think of Corbett in that clip. I've seen amateurs with better skills.
I watched this fight again. Just as I remembered, the 6'3, 232-lb Maskaev was pumping fairly stiff jabs into Tua's face throughout (thanks to his 9-inch reach advantage). Even swelled up Tua's face a bit with a very hard right hand in the second round. Won most of the rounds but still took some hard hooks and rights from Tua from time to time, including several hard body punches. Tua was on top of him for most of the fight but seemed reluctant to open up because he didn't want to open himself up to Maskaev's straight punches. From what I've seen, Corbett doesn't have nearly the work rate or power to deter Tua in that manner and I doubt he would be able to weather even a few of Tua's huge hooks the way Maskaev did.
If i had to wager a guess it would be that we are dealing with the small man syndrome here and those that are siding with Corbett aren't exactly giants if you get my drift. Seen it all too often, really no point in attempting any rational debate with anyone who is vertically challenged and not very muscular as they really are the most stubborn individuals.
maybe i just think the guy who has better stamina, speed and experience of long bouts has a big advantage in a finish fight? 12/15 rounds i'd pick tua in a heartbeat.
i've never played tennis but i pay the bills betting on it. the ring size matters, and it's possible tua does him early, but since stamina is huge in a finish fight i don't see what's so ridiculous about picking the guy who actually fought under this ruleset. corbett doesn't look so good on film, but he obviously had the physical ability to make it work to a decent standard in his prime.