Okay, imagine the following rules:
from 2013 on, in RG all the players MUST PLAY WITH EXACTLY THE SAME RACQUET, for example the Prince Original Graphite.
In Wimbledon all players MUST PLAY WITH THE WILSON WOOD RACQUET.
In the USOPEN all players MUST PLAY WITH THE HEAD PRESTIGE.
In the AusOPEN all players MUST PLAY WITH THE BABOLAT AEROPRO DRIVE.
In the next 10 years you won't see players winning 10+ GS under this scenario.
Would you then say that these future players were "WORSE" THAN former 10+ GS winners players?
They would not be worse, they would simply be from a different era where it was much more difficult to win a high nš of GS tournaments (because of the variation of conditions).