The thing about Oath decks is that you don't want to use too many creatures, because you rarely want to draw creatures. They're dead weight unless they're small enough to cast. That's why Treetop Village is so good. It doesn't count as a creature. I am not exactly sure how this deck runs, but I've seen other builds and some of them do pretty well...
I am not sure about Terravore. He could be really big, but what you're probably hoping for is a Gurzigost. You might Oath, and then end up with a Terravore after five cards, and not all of those cards are going to be lands. I mean, that's pretty extreme, but it just doesn't seem worth it. Gurzigost is much more forgiving if it's near the top, because it doesn't need that many cards before it kills them generally and it can eat from your hand with a little mana...
I would definitely use Swords to Plowshares. It is fertilizer if you're up against a creatureless deck or a deck that chooses not to drop creatures, but so is Oath, and you can afford one other card like that, although Oath doesn't like facing some creatureless decks...
Most Oath decks (non-turbo, that is) use a rather impressive countermagic base, the reason being that you need to stay alive until you Oath, or have an edge if you don't. Treetop Villages and hardcasting Gurzigost would be the alternate kill here (and that is why using something like Plated Slagwurm, Tornado Elemental, etc. is usually not so great--it has to be Oathed up because hardcasting it would be absurd). But anyway, I just don't think this deck is disruptive enough.
Now why Reclaim instead of Regrowth? On a less important note, while running white, I would consider Seal of Cleansing over Naturalize, but it probably doesn't matter, and Naturalize might be better in this deck anyway...
I am not sure about the Groves either, but I've never seen them in action...
Terravore is probably good in one of two situations.
1. You are able to Oath and you dump nearly half of your deck's lands into the graveyard (nine or so should do it, and that's almost half of twenty-two).
2. It is sitting in your hand and Fluctuator chooses to go off, but has to wait a turn for the kill. Okay, so any situation in which your opponent does the work for you really...
Instead, I would consider simply using that slot on a noncreature or using one of the self-sacrificing creatures the old Oath decks liked (since if frees you to Oath up something else).
I've suggested a lot here, and some of it is probably wrong, but I think the most important thing is the disruption. Your countermagic base is kind of tiny, and you need to be able to protect your Oath, your creatures, and yourself...
