Let's say you have 3 of each god card in your deck. You need monsters as tribute in order to summon them–and keep in mind, each of them require 3 tributes. If you draw, in your opening hand, 2-3 god cards and 2-3 of anything else, chances are you're not going to be able to put those on the field, in the first turn or so, or any real timely manner. More likely than not, you're going to get OTK'd. On the flip side, if you begin with only monsters meant for tribute in your hand, you probably wouldn't do too well either. You'd want a delicate mix.
There are some ways to cheese them out faster, but for the most part, you'd really only want to run 1-2 copies of each maximum, maybe 3 Ra - Sphere Modes, since you can tribute your opponent's monsters to summon that one.