You can't WAIT for your Graboids. You must get the offensive power quickly and then control them in later game. I would replace 2 Lightnings with 2 more of them.
Next one. Not too much defense here and probably that's why you lose against AI5. I would rather replace SoGs (yeah, because 3 SoGs in a deck is rather too small stalling power) with some more Dim Shields. They're one of the best shields in the game after all.
One more thing. If you can't get a next Poseidon, get some Earthquakes. More pillar control gives you some more time to get your strategy started.
That's only my opinion, but I think it is what this deck needs.
Then it would look like this:
4 Novas
10 Stone Pillars
6 Graboids
2 Enchants
1 Mind Flayer
1 Nymph's Tears
5 (or maybe 1-2 more) Aether Pillars
4 Dim Shields
2 Quints
1 SoD (or you can get some more)
1 Poseidon
2-3 Earthquakes
The deck would contain about the same amount of cards if you'd add + Pillars and SoDs. Without them, it'd be smaller and maybe more offensive.
In the future, I would be more Poseidon-based. 1-2 Poseidons more, maybe even Novas replaced by Sapphire Pillars and then change the mark to time for the Graboids. (don't kick me if it's a bad idea, ok? :/)