You are looking at the skill one-sided.
Have you seen 32 heal tiles from cleric c3 that basically keep your team at full HP all the time? Safety zone = gg meteor gg snipe lolz
On priest tree, monstrance give +30% DEX for whole party, revive = gg lolz never die. And of course stone skin
On krivis tree, aurukas = you miss miss miss, zacial = we crit crit crit
On diev tree, world tree carve = no spells lolz, laima statue = spam all day long
Plague doctor is just vastly better than the other rank 7 choice in PvP, hence the popularity, especially when you can choose plague doctor ON TOP of those classes.

