First of all, just wanted to spam the boards and say that this article is yet another reason to get SCG Premium (shameless plug), and a good promotion of Vintage, so keep that up.
As long as Oath has existed, there has been the desire to find the ultimate Oath creature that would win the game more efficient and effectively than what has been used before. We can call this the 'ultimate creature' panacea, the idea if that we could just find the right oath creatures, we'd be fine.
In that vein, we've see many creature progressions over time, and breaks in that progression for different strategies. Back in the day, people used to use cards like Spike Weaver and Morphling, then my team innovated Spirit of the Night and Akroma (with sb Pristine Angel), which later evolved into Hellkite Oath, broken up by Tyrant in the Gush era, and most recently we've seen Iona, and then Iona + Terastodon.
While this is an important evolution, I don't think the fundamentals of the deck have really changed at all. By that I mean that the fundamental structural limitation on Oath is 1) finding, 2) resolving, and 3) triggering Oath of Druids. Nothing in the card pool has changed that fundamental limitation in quite some time (arguably Orchard or Ponder was the last). The restriction of Brainstorm has only made that constraint more limiting. And the printing of Nature's Claim, and its heavy use, only makes (3) more difficult. In that respect, I'm not sure that this is an improvement on other lists.
While 1 creature Oath lists sometimes seem like an improvement, and greater focus, I think their drawback and liability is not to be underestimated: that is, naturally drawing the sole creature, or having your creature untimely removed. For example, you only half a dozen cards or so, not enough to really get the bonus, and someone plows the Titan. Or, you oath up your whole library, enough to get the bonus, and someone plows your Titan, but counters Reclamation, or resolves Null Rod, etc. It's not that any one of these things is likely to happen, but if you add up the sum total of everything that can go wrong, it's definitely nontrivial. It's not that it's particularly likely, for example, that you'll draw Sun Titan in an otherwise excellent hand, and can't seem to put it back very quickly, but it's that plus all of the other things that could go wrong that make me wary of one creature oath lists.
I see alot of vulnerabilities in your list, despite your excellent attempts to find answers for them. Now that this is out there, it will be interesting to see if people try it, and if they do, how they fare.
Incidentally, I went back to my M11 set review, to make sure I mentioned Sun Titan, only to discover some relief:
Sun Titan
It has some niche applications in both Oath and Dredge, since it can find Time Vault or Bazaar of Baghdad, and put it directly into play, to dredge the rest of your library, sacrifice it to Cabal Therapy or Dread Return, and do it all again, if need be. It’s Vintage playable, and will likely see some play.