RDM is, in my opinion, one of the worst pvp jobs in the game currently. It's horrendous in frontline, and mediocre in feast, and I hope the devs take note and give it some significant buffs in the future.
I think their biggest problems are:
1. They're GCD locked. They have no source of significant off GCD damage, all of their damage comes from GCD spells/weaponskills. This wouldn't really be that big of a problem, BLM is similar in that respect, but the difference in BLM spells hit like a truck and they can pump out Fire IVs consistently. RDM just doesn't have the damage to justify having no off GCD damage source.
2. They need to go into melee range to deal max damage. Ranged jobs have the lowest HP and generally weakest defenses out of all roles, so going into melee range is almost a guaranteed death sentence. This is easily seen in Frontline, where RDM are easy pickin'. You can kind of play around this by preparing the first 2 parts of your melee combo, and then only gap closing onto your target to use the finisher + verflare/verholy and jump back, but that means you're basically wasting the first part of your combo. For a ranged job that's required to go into melee range, I feel like their melee combo should either deal more damage, or come out significantly faster, because currently it's just not worth the risk.
They have other problems too but they're not as big as the first two.
3. They have the worst self sustain. I find this one kind of funny because RDM is a job that has an actual, really good curative spell in their PVE arsenal, whereas BLM has none and SMN has a significantly "meh" one. Of course pve should have no bearing on pvp balance, but the other two casters have ways to heal themselves. Yes, even BLM does for those that don't know. Convert restores 25% of their max HP and MP, at the cost of dropping Enochian. SMN has Energy Drain of course. So now we have a caster job with no way of healing themselves, throwing theirself into the enemy team. I think some form of heal wouldn't be too much to ask for. It could have a cost in the same way SMN and BLM trade damage for self-sustain.
4. They have the worst CC of all ranged jobs. Their only form of cc is heavy, and it's aoe. That's actually not too bad on the surface, but once you take into account the fact that it's on the GCD and requires you to be in melee range to use it....Yeah. The least they could do is make Flunge off GCD so that when they jump in it's harder for their target to get away, I think it's only fair considering the risk that RDMs put themselves in.
Some quick fixes I can think of is just increase RDM damage overall if they want to keep them GCD locked. Maybe a slight increase on jolt/impact on their Ver spells, and a significant damage increase to their melee combo to make up for the risk. I think Flunge should also be off GCD, too.