How did Tyson even survive...

[Lance Uppercut]

The era of the super heavyweights did not begin until the late 90's

[Spicoli]

Primal instincts and top notch reflexes and speed.Also the influences of Cus,Teddy.That era of Heavys was clutter waiting for a bad ass with a broom.His stubby legs were like coiled steel,springing under most guys early on and leaving them detached from there senses.

[Dark Lord Al]

The era of the super heavyweights did not begin until the late 90's

That is correct , and Tyson's oposition was poor , ageing former champs / light heavies( Spinks ) and poor fighters like Tyrell Biggs.

[Mikkel_K]

The era of the super heavyweights did not begin until the late 90's

Lennox Lewis and Riddick Bowe were both pretty big.

To me the 'super' era really started there (e.g. the early 90'es), although subsequent boxers were even bigger. Of course Tyson didnt fight either of them in his prime, and he did not really 'dominate' the divsion anymore when they came around either.

Also, it is worth noting that before 2000 Tyson only fought three fighters weighing in at 235 or more. And Sammy Scaff, Mike Jameson and Bruno II weren't exactly the biggest threats (pun intended) to him to begin with.