Melees just need good stats to do damage, once you get some items that give +str/agi their damage and special effects goes way up. My Gaulen cripples the enemies with the wounds his axe does and is one of my better dps'ers, thief doesn't hit that hard but daggers attack quickly so it adds up. Bard is ok later, early on the songs are too short to be very useful. I regret not having a mage though, I'm at lvl 19 and my team still has no AE or burst damage to speak of. Divine Summoner is sometimes great but enemies who do a lot of AE or attack the back row can kill off her summons and then she's completely useless. At least I have a paladin, a healer with infinite mana and AE heals and a huge group +def/evasion buff who melees decently well is great.It's okay. I feel some classes are underpowered massively, at least early. Pretty much all my damage came from my mage and barb. Gaulen, bard, thief did literally nothing.
It's the usual CRPG annoyance - once you know how to make the perfect party you've played so long you can't bother to reroll.