It's the point that you counter the one, but the three other Dark Knights yonk you. You can only purify so much that fast. I've been yonked 3 times in a row, turned into an imp, and charmed by a Dancer all within seconds of each other. Sure, you can stop one on their own, but not all that. And sure, you could argue that if you got hit with that much, you should die. And I don't disagree with you. Sometimes, you get mobbed by the enemy team/teams. But there's something wrong with the amount of stuns and how they can interact and stack with each other. Again if your whole team gets salted earth and in that moment they get spam limit breaked and they all die it's frustrating, but you try to move past it and stop clumping up, but when it happens multiple times a game it's an issue.
Personally, I think Salted Earth and Imp need to be a limit break. Something that isn't so easy to use. And maybe have purified nullify the stuns for x amount of seconds.
This isn't competitive pvp. This is casual pvp. The majority of people are doing it for the experience boost and the series xp. Nobody is 50-0 killstreak engaging in casual pvp and if you're then that's on you, but they really need to look at who is actually playing the pvp and service them as customers before they figured out more ways that skilled players can take advantage of your average Joe's.
From what I have played in pvp, I don't think SquareEnix knows what they're doing, to be honest.