Of course, thicker is better...
You are right, thicker is better, but some of the thickness of the tank is required for structural integrity and it's not done the same way, they used chopper guns which shoot fibers laced with resin, the same way it is done for boat hulls. The chopped fiberglass has less structural strength than woven cloth, that is why it is thicker (they also had to account for some idiot sitting on the tank trying to get the back end lighter to burn up that rear tire and this is something I will never admit having done in my early years of ownership of my 1969 blue Commando S :lol: )
What I would do is open up the hole by grinding a very gradual slope, then put as many layers as it takes to get it flush with the original bottom, then sand the surface smooth without forgetting to fix whatever caused the hole in the first place.
Jean