Yeah, Gothitelle is pretty retarded. Notice how I'm not even using the word "broken" here, because that would be an understatement to how completely retarded it is. It makes using anything but offense bad, and a metagame where only offense is viable is most certainly an unhealthy metagame. Gothitelle can trap and kill pretty much everything on a common stall team. The Choice Specs set is the best for this job, since between Psyshock, Thunderbolt, and HP Fire, you can beat pretty much every wall in the tier. Slowking, Roselia, Cryogonal; all these top-tier special walls can't touch Gothitelle. The fact that you're forced to carry a Pursuit user is another huge part of the problem. There are really only three common Pursuit users in RU: Spiritomb, Escavalier, and Drapion. Having to run one of these three on every team you make is stupid, and is pretty much what overcentralization is about. Escavalier isn't even foolproof to Choice Specs set, because even if you do double switch to it, you get wrecked by HP Fire. You can't play around Gothitelle, since it's too bulky and powerful to be beaten by anything on a common stall team, since you can't switch.
Gothitelle paired with VoltTurn is ridiculously broken, since there's literally no way around it. You basically get something with U-turn or Volt Switch in against a stall team, and it's a guaranteed KO. There is no need for prediction with Gothitelle. You come in, you 2HKO something. It's that simple. Once again, the fact that you have to use Spiritomb or Drapion on every team to stop it at one kill is retarded.
While SubCM isn't necessarily the best Gothitelle set, it's much more retarded than the Specs set. It basically gets three kills with the help of Memento spam (which is pretty retarded in itself), and can bypass even Drapion and Spiritomb. You just simply can't stop it from getting up to +6. It's incredibly simple to get something to -4 with Whimsicott and Diglett, and then Gothitelle sets up for free and destroys your entire team. Memento spam dominates the ladder, and it's such a ridiculously retarded and easy-to-use strategy all because of Gothitelle.
You can't really compare Dugtrio to Gothitelle, since Dugtrio is so weak. Only Pokemon that are especially prone to being picked off by Dugtrio, such as Tyranitar, would even consider throwing on a Shed Shell. Dugtrio can't even 2HKO Blissey with Earthquake. The problem with Gothitelle is that everything is especially prone to it, so you'd have to stick a Shed Shell on literally everything, which is obviously stupid for a healthy metagame. This isn't even taking into account that the two best defensive Spikers both use Eviolite. Others, like Slowking, can't afford to give up Leftovers, since they need the extra HP to check Moltres and Nidoqueen better. Others, like Lanturn, have no form of recovery otherwise. And then there's things like Cryogonal, which is probably the most important thing on your team to keep alive in a lot of battles, and has a lot of pressure since it has to take on Pursuit users as well as top specially attacking threats.
It wouldn't be absurd to run 6 Shed Shell Pokemon on a stall team just to "adapt". Or 5 Shed Shell Pokemon and Choice Band Spiritomb. This is really a no-brainer to me, why would we even want to keep Gothitelle in the tier? There's literally no benefit to it if we want a healthy metagame.