Eh idk; snipers are probably the most underrated class in the game right now and can do insane damage from 30 yards away, are unchargable, and have leg shot + a knockback to keep you away. Sorcs are pretty squish, but the amount of tools packed into that class is insane--most sorcs are baddies though so they try to fight melees IN melee and get punished. Mercs are the only real class I honestly feel a little bad for. No interrupt, good mitigation, but I feel like they do nothing to me--I just interrupt their tracer and dance around them; they might knock me back and pop a shield that allows them to live a lot longer, but they are finished.
Ranged classes are always the easiest to PvE with, but usually harder to PvP (at least from my perspective from playing different MMOs) with because they require careful positioning and lots of kiting. You can't fight a melee in melee as a ranged--you will lose. Because a melee can't have the uptime of a ranged, they deal a lot more damage but are more susceptible to slows, roots, etc... and need to be in the center of a fight while a ranged guy can stand 30 yards away and dps away.
Melee are too mobile? I don't know if I can agree with that, no dps spec has a grapple (except powertechs maybe?); and the rest have 1-2 abilities max to close the gap. Marauders have charge (they can use vanish offensively but then you can punish them as they won't have it to escape). Juggs have charge and force push which refreshes charge, but probably have the lowest PvP damage in the game of any dps spec. Operatives have stealth. Assassins have stealth and sprint. Powertechs have a charge and a grapple. I really don't see the problem. Most ranged classes in turn have 2+ abilities to deal with gap closers or an annoying melee.
I'd say the problem with PvP, if any, is the lack of rated warzones. Regular warzones are a mess because the gear discrepancy increased exponentially with this patch (battlemaster vs recruit/champion is HUGE), and all the battlemasters are stuck in regular wz's waiting for rateds. Once we get rateds, we get regular wz's for fresh 50s, alts, and decently geared peeps; while the coordinated groups of BMs move to rateds where we can see strats start to develop and get a better look at what truly is overpowered and uncounterable and what is just a pubstomper spec/class (operatives are probably the biggest example of this--I'm going to say they will be one of the weakest rated dps, but will still absolutely destroy regular warzones becaue they are pure gankers designed to win 1v1s and piss you off).