Frazier was incredible in his day, his style was awkward (as Ali found out) his power was immense.
He fought the best on offer at the time, Machen, Bonavena, Chuvalo, Quarry, Ellis etc before beating Ali in 1971. Only big George really demolished him and i think the first Ali fight took a lot out of him.
He deserves full credit for a great career and he would have beaten most of the guys mentioned.