What keeps Hoopa-U from being one of the most used competitive Pokemon?

Question

Hoopa-U seems to be a totally overpowered abomination. 680 BST, offensive stats nearly rivaling that of Mega-Rayquaza. A solid choice of moves, access to boosting moves too. Low speed to take advantage of Trick-Room. Access to a handful of high base power moves. Magician isn't a bad ability either, and it only has one weakness, to a lesser-used type.

I get that Hoopa-U is in Ubers (I think) but at this point it feels like something everyone would want on every team.

Comments

What generation? Also, the answer is at least partially the omnipresence of U-turn.

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All generations since introduction, I suppose. U-turn is a fairly good reason I overlooked, but still. Hoopa-U is more of a wallbreaker anyways, although I feel it could be a fantastic sweeper.

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In Gen 9, Hoop-U is currently in UU. While it is a scary threat, the things that hold it back is U-turn existing along with not having a good defense stat.

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I guess it having a mediocre speed stat also doesn't help it either.

Answer 1

To quote's Hoopa-U's Gen 6 and Gen 7 Smogon analyses, the reason is this:
Gen 6 Ubers analysis

Despite that, however, its viability should not be overestimated, as
stall is the least solid playstyle in Ubers and Hoopa-U is vulnerable
to all forms of status and entry hazards. In addition, Hoopa-U is
hindered by its mediocre Speed and pathetic Defense, which leaves it
susceptible to physical attackers and priority moves.

Gen 7 OU analysis

On the flipside, its middling Speed stat, despite being good for a
wallbreaker of its caliber, leaves it at the mercy of a number of
faster offensive threats in the metagame such as Mega Medicham,
Kartana, and Tapu Lele. It also carries poor physical bulk along with
a 4x weakness to one of the strongest momentum-gaining moves in the
game, U-turn, meaning that Hoopa-U tends to get overwhelmed by the
likes of U-turn Tornadus-T, Greninja, and Tapu Koko.

In short, the reasons are as follows:
1. 4x weakness to U-Turn is a severe downside, means it gets revenge killed by a lot of offensive threats.
2. Mediocre speed and pathetic defense means it easily gets revenge killed by faster offensive threats.
3. In the case of Gen 6 Ubers, stall-breakers not being in very high demand.
Source: https://www.smogon.com/dex/xy/pokemon/hoopa-unbound/
https://www.smogon.com/dex/sm/pokemon/hoopa-unbound/

Comments

Oh so that's why it went down to UU in Gen 9

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Hoopa was added to gen 9 recently, right? There's still a good chance that it can go back to OU.

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Perhaps. It depends if players find a way to make it useful to counter common things or attack with brute force effectively.

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I personally think that Hoopa-U will be better in doubles, atleast more than singles.
Its signature move breaks through protect which is everywhere in doubles but barely in singles (except on toxic stall). And U-turn while still fairly common in doubles, is not as common as singles.
It is too slow for its horrible defence but it can be useful (more useful than singles). One set that I liked was Choice Specs-Expanding Force with minimum speed alongside TR Indedee in DUU.