Relatively to the Covert Cloak Gholedngo set being a dedicated set, I think we reach an agreement, we both agree that the item has more purposes on Gholdengo than being immune to Salt Cure, despite that being its main purpose, the same can not be said, however, about other Covert Cloak Pokemon like Corviknight or Skeledirge as you say.
First of all, a big part of Corviknight's relevance actually has to do with absorbing Knock off and u-turning out to achieve momentum. If u are running a covert cloak set with iron defense, that cant achieve momentum (and still loses to the rare Tera ghost curse set), you will be playing a 5vs6 match-up most games. What is the point of running Corv just for Garg when u cant Switch into Tusk, Meowscarada or Iron Treads? Its just a dedicated set that is deadweight in most match-ups.
Skeledirge is no difference. You said that Garg needs a lot of team support to beat Covert loak Skeledirge but thats just not true at all. If you are switching Skeledirge into Garga and ur opponent has a default Garga set, it gets up rocks on Skeledirge. In case you try to go to tusk, Corv or any other Spiner to remove hazards, Garga just Teras and beats them 1v1 Forcing Rocks to stay up. With this, Garga just has to spend 1 salt cure pp every time Skeledirge comes in to absorb salt cure, making it take damage from stealth rock and switching out the next turn.
Skeledirge runs out of slack off PP way faster than Garganacl runs out of salt cure.
Even in a scenario where u manage to trade hazards Garganacl simply has more longevity than Covert Cloak Skeledirge due to leftovers recovery and not being weak to Stealth Rocks unlike dirge. Even if you tera Dirge to take less damage from Stealth Rock, Earthquake and Salt Cure u just lose because 8 Slack off PP is not enough and because Garganacl may simply bait you in and not actually click salt cure long term to force you to take Stealth Rocks damage.
Skeledirge beats garg with ease using EP. After +2, Garg is forced to switch, be basically dead, waste a turn to recover allowing you to +3 guaranteeing that KO and making switching risky or what not. Curse is wasted on Unaware and allows set up, and even if Garg recovers Dirge can continue to TS to boost damage until it's guaranteed death. Rock Salt on cloak on slightly higher def investment takes approximately ~20%. Keep in mind this is with 0 SPATK investment. If you switch Dirge on Garg you shouldn't be switching to a spinner instantly. It can wait, priority targets matter more than just instantly switching. KO Garg or force it out then go for RS. Like if everyone goes for EH removal immediately this sets up GT/etc. to be Iron Valiant snacks MB goes BRRRR.
If it's lead (SR) Garg, just switch in Dirge before rocks hit the field or if it's not lead when it's switched in just in case. Even then Garg has the same weaknesses (if not worse) than Dondozo has. Hilariously, Dozo and Garg share quite a few weaknesses outside a few specific teras.
Just to make a case in point:
Fairy Tera loses to TS from Dirge. Flying Tera loses to TS from Dirge. Ghost Tera loses to TS from Dirge. Poison/etc. lose to TS from Dirge. Only water, default, dragon and fire don't lose to TS. Those specific types lose to EP.
If you don't have something to beat water how does your team manage Dondozo? If you don't have anything to answer dragon how does your team answer Dragonite (Now I'm starting to see why so many people had problems with DNite), and default and fire share the same weakness, how does your team handle Dirge in that case. EP handles water, dragon, fire and default btw. Shadow Ball is not actually required in OU for the most part on Dirge. Gholdengo gets devoured by TS, and EP is great mirror match Dirge if you tera outside of Ghost. Dragapult out speeds you anyway and EP is neutral and allows you to thrash Pex.* Note I've never seen dragon/fire/poison/bug/ice/normal/etc. Garg.
In regards to switching, Garg often stays in, and by the time it should switch you're already rolling a +2 dirge. Which means most switch ins aren't going to want to risk it even on resist or you can mind game predict the switch and hit them with SB/EP. At most by +2 you should have only used one slack off by then. Let's say you +2 EP Garg, even if it survives and switches out it's going to be below 40% quite often which makes it fodder for quite a few special attackers, Great Tusk (regardless of Tera HR/CC/Knockoff is coming to do around ~45% depending and that's without CB) and what not and if you have hazards up it's going to be ~30% health at best. If it's switched out it isn't RS your team, so it can't be this impossible fortress and guerilla tactic mon at the same time, it's either one or the other.
In regards to Dirge though:
So Garg Tera doesn't stop dirge, trying to stall Dirge doesn't stop dirge, RS on cloak doesn't stop dirge (and even without cloak it takes max ~30% a turn RS+RS extended damage) *Note it only takes ~30% on turns where Garg doesn't ID/Recover.*This assumes it isn't ATK investment Garg which takes even more damage. which should only take around 2~3 SO if running anything but cloak. assuming it doesn't switch out. If it does their switch is taking a +2 TS or EP depending and isn't going to be too happy. Even if you go with team support argument, Dirge can easily be supported as well and be brought back out later to finish up it's delicate but rocky meal.
