Be honest, do you PvP in a ranked setting?
Sure, if you have a healer, you can tear things up.. but so can every other class. The difference is, other classes can tear things up without a healer. Plus, a rage spec'd Marauder or Jugg will unleash quicker, larger damage than any Merc/Commando could.
A "perma"slow isn't utility. Every other class has a form of slow with relatively low costs, cooldowns and/or in a passive form from talents. Also, massive AoE damage doesn't matter, because anyone who's competent will move out of your AoE as soon as they see the circle on the ground. Again, your class has nothing unique compared to others, and other classes do your job better. Rage juggs/marauders do massive aoe also, and it's instant, + it can occur rather frequently. There's nothing that redeems mercs/commandos at the moment.
I do pvp in a ranked setting, probably not as often as I should admittedly. But mercs are the jack of all trades masters of none. I like those sorts of classes tbh. Most of the "Best dpsers" can not heal at all, and in pvp a dps merc tossing a soft heal or two can really throw off an enemy team to the point they mark you as a healer and leave your healer alone.
Like I said, I don't see a problem but that is just my PoV you are entitled to yours.
I will never advocate against a free buff but I like that I'm one of the few Mercs in pvp anymore, makes me feel special.