Why is Doyle Brunson considered to be so good?

[Shootmeplease]

Dont get me wrong, I;m sure twenty years ago Doyle was one of the best ever at Hold'em when noone knew what they were doing. Now everyone studies and knows everything. Back then he had noones to play against today he has people like Negraneua, Tuan Lee, Jamie Gold, Allen Cunningham and so on. These guys are fearless and would tear Doyle apart in the long run.