1) Ranged is OP at high skill and UP at low skill.
A) Targeting is the hardest part of FFXIV PVP. Knowing who to hit when and being able to acquire the your target is vital. If a target can't be acquired by everyone, there's no point in the team hitting them at all. This means a skilled player will always focus certain roles based on ease of targeting.
B) And ease of targeting means melee jobs, but many of those jobs aren't really appreciably tankier. The defensive CDs most melee DPS get aren't strong enough to compensate. SAM for example can reduce damage taken significantly, but it only lasts 5 seconds and has multiple uses. Their barrier only applies if the skill hits 2+ people AND it has a cast. This makes them an excellent candidate for focus fire.
C) While melee DPS can eventually beat most ranged in 1v1, 1v1s pretty much never matters in serious play. The only strategy that works is an entire team hitting one person to get past the ridiculous defensive kit every player has. Trying to disrupt the backrow assassin-style is pointless.
All this combines to create a meta where ranged sit back and wait for melee to die. Which brings us to our next problem...
2) Roleless queueing means that in higher ranks where skill is predictably competent battles are won or lost before they're ever fought.
A) There's basically no strategic complexity in Crystalline Conflict, the goal is always the same. Reduce their numbers before they reduce yours. So battle is all that really counts and the problems from (1) really start to shine through.
B) If there was a draft-pick style way to select your job you could try to compensate for your team's poor synergy, but there is not. Some team comps simply do not work. If you put a samurai on a team with 4 ranged, she's going to get focused down and die and basically be worthless because the rest of the team will be untargetable making that component of difficulty null and void. And once she's dead it's a 5v4 and her team will get steamrolled.
The problem isn't class imbalance primarily (though this is an issue). It's the innate advantage of ranged damage and how it shapes the battle. There's no point in going after them for aforementioned reasons, which means it's all about which frontliners go down first.
3) The lack of player agency over the shape of matches means the meta pretty much can't be disrupted.
A) You can't communicate ingame to suggest doing something weird that plays to your team's strengths.
B) You can't queue with your friends to practice these strategies. Even if you could, you can't queue with your friends to USE them.
C) To win you need to play classes that fit into a winning strategy, which just further reinforces everything boiling down into this.