Negative resistances didn’t increase harm. PVP gear had no shadow immunity, pve equipment had around 100 that is annoying but not the gold wow classic end of the planet in PVP, if they needed to counter exact player, res gear was used by people in PVP. Besides nobody employed CoS in pvp because agony is by far you best dot and CoT/CoEX are simply better in any possible situation, and should you rolled destro you just used CoE.
Reason why Lupus did harm he did(which can be wrongfully appointed to do something together with resistances) was him doing shadow harm and eating up critical shadowbolt debuff that made every warlock in the raid mad as hell of hunters with this stupid wolf.
Even though two of the top ten abilities you showed us were Shamans (Frost shock,Windfury) people have false thoughts about Vanilla Shaman due to the videos out there showing completely geared hybrids one shot people with WF procs.
The truth is that Shaman wasnt so good back then,was pretty RNG in PvP based on Flurry and WF procs,had a lot of gear to be considered strong competitions,equipment that was really impossible to have in ancient patches since the gold in wow classic one thing you used to do was recovery in raids and never have priorities about getting your hands on DPS gear.
If you was able to perform as Enhancement or reunite in the days,you would largely never fit in a raid essay since you wouldnt even be at a good dps range against Mages,Rogues,Warriors or Warlocks and nearly all of your raid buffing totems might also be used by a Restoration Shaman who was among the most useful specs to play Vanilla.