It is less powerful than it's SL/SL tbc version, but the durability is insane, especially when geared.
It can hands down outlast any other class/spec as long as they don't out gear you drastically, all those fancy pvp videos you see of mages and rogues mean nothing to you coz they downright tickle with proper pet management + drain tanking, just make sure your pet isn't banished.
Heck you can even outlast tanks due to sustain and can drain a healer dry of their mana , though in most cases no one will want anything to do with you once they see you're soul link spec, and you're slower than a moving turtle with no tools or enough dmg to kill something fast enough or stop it from running away.
In other words you are quite literally the best pvp tank in the game with the worst mobility possible, this is further emphasized with gearing ( more stamina heavy build instead of raw spell damage ).
As for talents/ rotation, you generally never cast Sbolt outside NF proc unless no one is attacking you, it's typically just dots/drain spec, if u get locked on shadow spam searing pain.
When do you recommend going to SL from SM/Ruin?? is it gear dependant? CoEx is so useful in WSG, I'll think I'll miss it