Is Exodia the strongest God card of them all?

No, for several reasons.

1. Exodia can refer to either a singular card or to a set of 5 cards. If you are referring to the singular card called Exodia the Forbidden One without the rest of the set, it’s a 1000/1000 normal monster that can’t even be treated as a normal monster for the purposes of effects. Which means it gets run over/destroyed by Obelisk and Slifer (by battle, and card effect respectively, and can be run over by Ra at great cost (or tributed for the effect of Ra Sphere Mode).
2. If you are referring to it as the set of 5 cards, well by definition it cannot be the strongest God card because it is more than one card.
3. In either case, it is easily argued that Exodia is not a god card. The term God Card typically refers to the original 3 Egyptian God cards (which were introduced after Yugi lost Exodia). They consist of Slifer the Sky Dragon, The Winged Dragon of Ra, and Obelisk the Tormentor. The definition of the term can vary depending on who you ask. Possible definitions include: anything with the Divine Beast-Type (mostly just variants of the original 3), anything with the Divine Attribute (as the previous, but expanded to include Holatcie), the Original 3 plus the Sacred Beasts from GX (rare but there are people who believe this), or the first two definitions using the anime typing (will include the Aesir: Loki Odin, and Thor). Most definitions of God cards are defined in such a way that would exclude Exodia.
4. Exodia isn’t that strong of a deck right now (with Pot of Greed and many loops being forbidden right now). The most meta-relevant god card I would personally say right now is Ra- Sphere Mode but even then it shows up only rarely.

Source: Quora.com
Credit to: Andrew Lin