Because obviously amateaur players had their own level and if you was an amateur it was not easy feat to achieve.
But that doesn't change a fact: Pros were on an much higher level, so to achieve an amateur Grand Slam doesn't show any kind of domination.
In fact, he lost 41 matches over 53 he played against Rosewall and Hoad in 1963. You keep ignoring this fact, but numbers speak clearly: 12-33 against Rosewall, 0-8 against Hoad. Is that a dominance?
What a strange concept of dominance you have...
Federic, I have the impression you seek problems that are not existent. I never denied that a pro Grand Slam has (much) more weight than an amateur one. But still the latter has some significance.