First off, I don't get why Ho-oh is even being brought into this. Sure, Ho-oh, just like Mence, is crippled by Stealth Rock, but let's not forget that it's 4x weak to it, meaning that if your prediction is on point, you can limit Ho-oh's options severely (really, if you can get Ho-oh down to 1%, it's only options are to shoot off a desperation attack, or Roost). Mence is not the same case. Salamence, who can bluff several sets at once, isn't limited to three switch ins (2 if you count SS / LO in Ho-oh's situation), so if you even if you manage to outpredict it and scare it away, chances are that it's going to switch back in once its main threats (Scarfed Steels, Skarmory, Blissey, etc) are gone and wreak havoc later in the game. In fact, I almost never see MixMence stay in for more than a single turn unless my team has been weakened to the point where it can sweep. In addition to that, Ho-oh's bulky as fuck, and definitely not slow for OU standards, so it's going to take more than outpredicting it to kill it off. Secondly, I don't think that "too easy to wear down" is a legitimate claim to keep Mence OU. Yes, residual damage is a huge portion of determining tiering, but if the above quote was the case, then I don't see why we're not suspecting Deoxys-L, or even Wobbuffet for that matter? Both are worn down by U-turns from Scizor, Flygon, and Infernape, and constant hits from the common OU sweepers (though, in the latter's case, you'd be trading a Pokemon for a Pokemon) as well as all forms of entry hazards. Mence isn't any different from either Pokemon since it too can be worn down easily if you don't give it the chance of switching in and staying in safely. Salamence's ability to be checked like any other sweeper in OU, imo, is the only thing that keeps me in limbo on its tiering.
In all honesty, I don't have a problem killing Mence, but the first time that it switches in, it feels like I'm placing my cock under a guillotine with a gun pointed to my head. If I don't act calmly and intelligently I'll either lose an important Pokemon on my team, and possibly the game all together if I just play horribly. Unfortunately, playing around Mence is incredibly difficult due to three of is most potent and common sets that it can bluff effectively: New MixMence, Classic MixMence, and DDMence. The two MixMence sets are played pretty similarly, but the methods of checking them are very different; to be more precise, one set doesn't trap itself to kill Blissey while one does - well, I guess Roost is another difference, but that only makes a difference when Mence switches into a choice locked resistance/ground attack. The DD sets are what make me paranoid about checking Mence, since a wrong choice will cost me a few Pokemon. Yeah, mispredicting against Luke/Nape can result in similar consequences, but if either Pokemon attempts to bluff a move (i.e Bullet Punch > Crunch; SD Ape), they're still manageable and don't require to be worn to 50% of their health in order to be finished off by a Pokemon that instantly becomes set up fodder for another sweeper (yeah Scizor I'm talking to you, fuck your Bullet Punch, I have a Suicune/Lucario/Scizor/Kingdra/Raikou/Jolteon/Jirachi/Gyarados/Rotom-A/Magnezone/Metagross that doesn't mind setting up in your face). On a smaller note, I have to admit that the Mixed Dancer is incredibly fun to play around with. The ability to bluff MixMence is enough to mow through most of OU, since most players rely on wearing it down with constant switches, healing off small damage, etc to come out on top.
Though, despite what could happen when Mence switches in, there's always a method of beating it, albeit unreliable... unless you theorymoned too hard when making your team and became set up fodder for another legitimate sweeper. In which case, you should be set on fire ^_^