Couple of points
1. Pursuit trappers (read: ttar and aegislash) are actually not uncommon on balance and stall. They cover a myriad of mons like the latis, mewtwo forms, and especially mega gengar. Trapping the latter is essentially mandatory for stall to even have a prayer vs parish trap sets.
2. Hoopa only outspeeds the staple geoxern set (provided no creep). Unless your opponent has a stroke and switches directly in on a gunkshot or nasty plot, I can't imagine a scenario in which hoopa will be in safely vs an unboosted geoxern and beat it.
3. Most of the mons you listed are primarily stall mons, which was already established is its "niche." The other two, Ho-oh an klefki, are typically on builds that wont give it more than one kill before revenging it, if that. For example, it can set up vs the arc-w on absolute control, but only after taking a decent chunk from judgment and getting revenged easily by ho-oh. Vs every other member it gets whirlwinded out, limited to one life orb hit, or outright ko'd. I challenge you to provide an example of a team vs which it does more than plot once, kill once, then die on the spot.
4. Baring cb ho-oh, scarfed xern and a few others, choice items are not as good in ubers. I could maybe see a life orb offensive set working on occasion, but the lack of speed and loss of move choice definitely rules out banded/specs imo. And scarf is too weak.
5. Even on trick room, I have trouble justifying hoopa over other mons. Trick room's niche is its ability to give bulky stall and balance breakers offense breaking power by giving artificial speed control, similar to webs. This is why mons like sd 3 attack pdon, offensive pogre, and slow sd arc forms shine in it. These mons can afford to be in trick room because they can take priority, take hits if they need to, and even set up if they need to. Hoopa can't take any priority baring giratina's sneak after rocks, and without set up can't ohko much at all without being revenged. Not to mention that this is already a shaky style because of how carefully you have to play the turns.
D might be a bit low, I'll admit, but definitely no higher than C- or C. It's role is just too minuscule and situational to make it worth a slot on the majority of teams.
