I have messed around with Wolves Den a little bit and enjoyed my time there as a MRD and more recently a MNK. Working on earning marks to get a set of gear for frontlines, but the queues, man! The queues!

I will definitely be trying frontlines extensively until I'm sure its terrible, which I don't think or hope it will be.

P.S.

RE: MNK not being able to hit targets - unless you have some legit horrible lag that would prevent you from doing anything Titan X+, it sounds like you might just be getting out-played by your targets
RE: Healers dying in 2-5 seconds - only if the DPS/opposing tank is phenomenal and you are god awful. A moderately skilled healer versus moderately skilled DPS/Tank will take about 3-4 minutes to kill. The match usually goes to whoever kills the opposing healer first, so your main job is survival.