I don't think they should touch Mystism. The dervish has a 25 energy pool with most of their attack skills and spell cost 10-15e. Balth Rage and Heart are great skills but I don't think they deserve overpowered status. I would increase the recharge to 12-15 seconds. 20 seconds is too long. These guys are made for pressure. At 12-15 seconds recharge that would put it in line with Sin recharges and war adrenaline gain.
You can't do anything if you can't catch the target. CoP will have to be changed and I like the suggestion from Minus Sign. Remove the "lose all enchants" from CoP and make it linked to attribute. Even if you make that change they will simply change to release enchantments.
I ran this build with a Guild that was rather noobs and it completely fell on its face. Its not as easy as it seems. Kiting will completely own the build. Wars don't want to mess with a dervish though
