I really can't say anything about Hoopa-U that hasn't been said in the last 20 posts about it being one of the best mons in the metagame right now. Specs has a grand total of zero switchins and isn't nearly as much of a deadweight against faster teams as many people describe, since it can go 1 for 1 against a verity of special attackers such as Alakazam and Latios. Also, your mention that "sets that have HSF are the best" is completely false, as specs is widely considered its best set right now. Just take a look at posts by almost any other member, they state it better than I do.I think Hoopa-U should remain A+. True that it's incredibly strong and pressures a lot of bulky and stall teams, but it's also pressured a lot as well, not wanting to switch into many things. Even with bulky and stall teams you risk being statused. And not to mention it's extremely weak to priority users such as t-flame, scizor, mega lop and mega cham and offense in general because even if it switches into a special move, it will still take a good chunk of damage. Also the defense drop on hyperspace fury(which the sets that have these are the best ones imo) makes it weaker to be pursuit trapped. I feel like this is a hit or miss pokemon. It's either going to do destroy teams or do nothing or next to nothing.
Also I think Keldeo should drop out of S into A+ or A. I never understood why this is in S rank. Yeah spamming specs scald is pretty nice, but that's all its got going for it. It's not that versatile and there are plenty of checks in the game to deal with it such as AV torn, latios, starmie, and celebi.
Also just noticed made this post while it was updated.
Keldeo is deserving of its S rank spot due to the fact that all of its "switchins" (Slowbro, Mvenu) Are really annoyed by burns. For instance, after being burned by scald, Slowbro struggles to switch into hydro pump. Celebi is the only one really immune to this due to natural cure, but it gets torn apart by a potential HP bug. However, the biggest reason that I think Keldeo is ranked that high is due to stupidly good defensive potential for a mon that is so excellent offensively. It actually finds switchin opportunities against many dark types such as Weavile, Bisharp, and Tyranitar as well as a plethora of more passive mons like MSable and Heatean and Scizor, the latter of which isn't even too passive. This forces the opponent to make plays instead of just relying on soft checking Keldeo, or they're most likely gonna lose a mon. Keldeo also packs nice versatility between Scarf, Specs, and Sub CM, although most of the time specs is the best. Overall, it's rather easy for Keld to whittle its own checks with scald burns, and the high amount of mons it can switch into while still having outstanding offensive presence makes it easily one of the best mons in OU.