So, for anyone who hasn't seen the Finale of Season 4 of the anime, at the climax point of Athem's Dartz, the latter summoned his strongest monster, the Divine Serpent.
This bad boy had infinite attack points, with Athem referring to it as having "Infinite Strenght" thrice
How did our favorite Pharaoh beat this beast ? simple, he activated the special ability of his knights, which allowed him to redirect Crisius' attack into Heremos, who then activate his ability to redirect back the attack at his fellow knight. This created an endless loop, multipling the strenght of the attack to infinity, as he then merged the three knights ito the Knight of Destiny.
The Knight of Destiny is and i quote "Your serpent's strenght may be infinity, but now there's a force beyond infinity."
So yeah, both of them are clearly High 3-A, but what has this to do with the god card ? getting to it.
The great Leviathan, as Dartz's god and who the former spend over 10 thousand years to try revive, should very easilly be vastly above the Divine Serpent, a beast the atlantian menged to summon relativelly easilly [Remember that the Orichalcos has the power to make monsters actually appear in the world, as swell as the fact that in same season monsters were stated as real entities residing in a parralel world] and that he was only able to bring out thanks to the power of the Orichalcos [which was created by the great Leviathan], specifically with Orichalcos Kyutora and Orichalcos Shunoros. So the great Leviathan scales to the High 3-A.
Lastly, the god cards were the only thing that could stand against the Leviathan and defeat it, with every other monster not menaging to even scratch it and getting one-shotted, so much so that the serpent even initially tried to flee once they were ressurected. Furthermore, their power had been required to revive the great Leviathan. So High 3-A for the anime god cards, the Creator of Light and Zorc.