This has been discussed many a time - from DRK, to AST, to DRG, to SMN.
It has been talked to death, but I'm bringing it up again because it needs to be highlighted: AOE IS KILLING PvP.
And sure, you can say "Oh, who cares about PvP? It's just bad game mode." Well, the problem with PvP is that majority of people queue into Frontline Roulette only to get flavor of the day but it actually leaves bad tastes in a majority of people's mouths, thus turning them away from the game mode because "it's too hard" or "I can't play".
But back to the matter, AoE needs to be hard capped in PvP. We've had this issue for how long? Since CC became a thing? Let's go over the factors that are causing people more frustration than enjoyment with the game mode.
DRK - Most notorious for group CC and a surprisingly 15y Draw-in and Bind combo that essentially seals your doom the moment you stack 4 DRKs or even just 2. Guarding against this is usually the answer, but when you have at least an AST and a SMN in the back you literally can nuke the entire team just with ONE good draw-in. It's dumb, and I know it's set for CC - but when it's in Frontline? You essentially have a job that's insanely strong when it comes to 24v24v24; heck, even 24v24 winds up the same way!
DRG - How many times are you going to keep buffing this job? Because the only thing I've ever seen from patch notes are BUFFS. NERF IT. Their LB is the strongest in all of PvP because not only does it provide a GIGANTIC shield for no reason, you also deal 80% or more of your target's HP - in an AOE. If that's not enough, let's also add in buffs! When this job is buffed, that damage becomes multiplicative(*insert Battle High and Soaring here*), and when it's under even one of those? You can one-shot and entire team. If the problem is DRG not being able to get out, then maybe they shouldn't force Elusive Jump into a Burst Rotation in the first place and make Wyrmwind Thrust its own button instead of buffing the **** out of the job.
SMN - I like the job. I may not play it, but I like how it's designed. It has CC, it has a burst rotation, and on top of that it has the choice of Damage Reduction Phoenix or big bad Bahamut damage. The only problem is when you stack these jobs in a party. Having 2/3 SMNs is enough to nuke an entire Alliance, flat out - 2 if you have Soaring/Battle High.
AST - While not bad on the surface, the problem with this job is again, uncapped AoE - as is the running theme here. Macrocosmos not only stacks a portion of damage, you also DEAL damage when you use it - and yes, while the dreaded DRK/AST/AST/AST combo is something everyone dreads in Crystal because of its ridiculous nuking potential, but what's more is their LB is really strong - making their Nuking potential even higher while NERFING the entire enemy. What's more, they provide a lot of buffs to the group with their cards, essentially ranging from Damage Reduction, Damage, and Movement Speed+Haste. They're a very versatile healer for what they do since they also can provide shields.
Also, there is Battle High scaling that is causing a lot of issues for people. Melee sometimes take an entire alliance to take down(staring at you NIN), while as SMN or AST you essentially get to nuke an entire party for free if you get the chance. It's not as bad with Soaring, but it's horrible with Battle High. If anything, you reduce Melee's DR and they need to have Tanks to enable engagements(who have high DR), though most of that is relegated to DRK just pulling everyone in. You cap AoE at 5, you don't run into major problems where PvP is essentially an AoE fest - you change it into how many people are getting hit by the same AoE(which is still an advantage, mind, but it doesn't really change anything in the long run due to damage scaling). Edit: OH. There's one more I forgot.
WHM - Ah yes. I forgot about this one. Fast LB that is an AoE Line that causes a whole Stun for 3s. It's very strong, and scales very high with Battle High/Soaring. They nerfed how often it comes up, but it's still a strong tool that is uncapped - at a giant range at that.
So, there you have it: Those are the *five* biggest offenders right now, and we need a way for people to understand how to counter them proper(DRK having nearly 0 Counterplay most of the time due to Draw-in, but it's not impossible to stop one).