The game is set early on, everyone knows the criteria for winning, which is total slams. How you get there is your business. If you want to do it with 20 slams on one surface go right ahead. It's a pretty big risk to go that route to achieving 20 slams, but if that's your strategy and you pull it off, Kudos to Ralph.

Notice that when people put up GS stats. on the screen, there is not even a hint that the distribution matters, most likely because everyone thinks each of the GS is worth an equal amount.
Personally I am probably like you, I prefer more of a distribution across the slams, but that's just my preference and I recognize it as such. But Imo not having an distribution requirement makes it more fair for the clay courters because growing up on clay and developing a clay court style is not conducive to other surfaces. In the all slams are equal and it doesn't matter how you get your GS total world clay courters can specialize and reap the rewards from specialization while at the same time forgoing their chances at 2 other slams. The risk/reward is built into this game of achieving the most slams. Look at federer, currently federer is the master at no slam (at best he is tied with two others at the USO) yet fed managed to get to the top by doing very well on 3 different surfaces. But at the same time fed's lack of dominance came close to hurting him and that's the risk he took with a game that worked well on many surfaces.
Getting away from your great on every surface to be GOAT requirement, if nadal starts approaching federer's GS totals, he will have already satisfied matching federer's worst result at a GS. Federer only has 1 FO and nadal already has at least 1 tournament win at each of the 4 slams.