Originally Posted by Fat Doron
Why is Dusclops E ranked where Cofagrigus is S ranked? I use Dusclops all the time, there's nothing else in the tier that works as well as a catch-all defensive pivot. I'd even go as far as saying that this holds true in the OU tier (too many pokemon are geared up to take down Ferrothorn).
Also, Claydol has a niche as (I think?) the only rapid spinner that can also run Dual Screens, which, combined with stealth rock, makes it taunt fodder like nothing else! Also a unique pokemon with a movepool which allows it to fill multiple support roles on a team while taking up only one slot. But mostly taunt fodder.
Because neither of those two are rather effective at what they do. Cofagrigus in the long run is bulkier, as it has a usable HP stat and reliable recovery (sorta). Any other Ghost may not be as bulky, but can also bring an offensive punch, which Dusclops simply can't - Seismic Toss doesn't exactly count.
It may seem Claydol has that niche, but very rarely will it find the time to accomplish multiple roles. It's simply too weak to this metagame. A vast majority of the top 30 Pokemon in UU can and will beat Claydol one-on-one. Claydol also have this terrible inability to switch in on anything bar a Choice Electric-or Ground-type move, which severely diminishes its ability to perform its roles. Good on paper, terrible in practice.