We will never know if Laver would have won all 4 in 1969had he played the AO and the USO on hard court. It's all speculating.
1962 was too easy in the amateur. Any multiple top players today would have won the GS given the same circumstances.
Tier1(goat): Federer; Tier 1.5: Laver, Gonzales, Sampras, Nadal, Borg;
Tier 2: Lendl, Connors, Rosewall, Tilden; Tier 2.5: McEnroe, Agassi