I knew I was being hard on Splice spells, but I stated beforehand that I was going to be. I thought about that for a while, and even though I can see people splicing at the Prerelease, when it came to judging cards I couldn't afford to take that into account. How does one pick a Tier for a card when you have no idea how many times it will be used? Add into that the fact that even someone that tries hard to splice a lot will frequently cast a splice spell only once to provide a base for another splice spell to splice onto, and it becomes too complicated. My solution of informing the reader that I was going to judge them harshly, as though they could only be used once, was the best solution I could come up with.
You're probably right about the Thief of Hope deserving a mention. By the time I got done with all 110 commons, however, I could barely think straight. When I made my list of gamebreaking uncommons, I focused mostly on those cards that would really break the game in ways that Thief of Hope can't.
I think that Thief of Hope doesn't quite merit a comparison with the Disciple of the Vault. The Disciple of the Vault earned the bulk of its reputation from affinity decks that had vast numbers of artifacts that they could sacrifice on demand as a game-finishing blow. The Thief of Hope requires you to play spells, not just put them into play, and since they're Spirits instead of artifacts, this will always cost mana. The Thief of Hope fills much the same function and has a large number of merits that the Disciple of the Vault does not have, but it isn't quite the same thing.