Spriests are in a better place than Warlocks right now for PvP but I don’t think Warlocks are terrible but they are more vulnerable.
Afflic and Spriest are similar but with Spriest you have to worry about cleanses, UA makes it nice that people can’t just cleanse your dots. Dispelling Spriest dots can really lower their output and I do it a lot when I’m facing one. On the other hand Afflic have a very annoying slow and can really burst after they are setup, doing some sick damage, but Spriest are able to dish out strong burst at any time once their cd is up, pretty intense as well.
Destlock can deliver those big hits that Spriest kind of can’t. It’s a different playstyle.
Demolock I don’t even consider because I think it’s a stupid spec for the most part.
I think if you really like Warlocks you can consider going one. The next patch is going to nerf Hpaladin, which is the meta healer right now and can reduce shadow damage by 15 percent, so that’s basically a 15 percent dmg increase coming for dot classes of shadow magic so Warlocks might actually be a lot more viable very shortly in arena.
Overall, Spriest is in a better place and therefore the safer choice…RIGHT NOW, but Warlock can receive buffs at any moment, they’re are still people doing quite well with them but they’re not in a great place.