No...it wouldn't be "virtually" impossible to beat a 7'7 fighter. In fact it could be easier to be a fighter that big than one 6'5 or 6'7. Look at the NBA and the best Centers of all time....rarely if ever do you get someone who is 7'0+ ...Kareem Abdul Jabaar is pretty much IT in terms of a guy who is that tall and had the hand eye coordination and athletic ability to achieve anything. Guys like Gheorge Muresan and Son Mingming and Shawn Bradley so on typically can't handle it.

Look at 7 foot tall boxers we've seen, or those even close to 7 feet. Where are the champions? Valuev? That's it and he was specially guided to his title, and he avoided guys who were dangerous to him....there's a reason he didn't fight Chagaev again, he got beat and a beaten giant isn't fearsome. His promoters only agreed for him to fight guys that he had a chance at beating.

Guys who are 6'5, 6'4, thereabouts, those guys are harder to beat because they are still athletic.

Look at Julius The Towering Inferno Long, look at Tye Fields....the skill just isn't there after a while.