And do what back? Starmie switches out and gets rid of burn, and, well...You're exaggerating how bad it is. It is bad, sure, but it has the small niche in being able to beat all of OUs rapid spinners using a specially defensive rest + sleep talk set. Honestly, I wouldn't say that it's any worse than something like Aerodactyl.
252 SpA Life Orb Starmie Hydro Pump vs. 252 HP / 252+ SpD Eviolite Dusclops in rain: 129-152 (45.42 - 53.52%) -- guaranteed 2HKO after Stealth Rock
Have fun switching your Dusclops into that! And I thought Jellicent couldn't spinblock Starmie effectively. Dusclops can't even switch in on its Rain-boosted STAB.
As for everything else, Forretress sets up all of its hazards on you, nobody uses Donphan, and as for Tentacruel... You could argue that Dusclops could beat it, but then again, when you rely on RestTalk for recovery, you are bound to fail at some point.