Tbh at the current state of the game pretty much any build works mostly because of how crazily overpowered gear/crafting is. Mages definetely have it easier at the beginning, at mid levels warriors start to outperform mages damage wise because of gear, lategame its kinda even (I don't get all the fuzz about late game warrior aoe dps, WW can maybe deal 1.5 - 2k aoe when buffed, whereas meteor storm can deal 2k+ per meteor, in a much larger area, with ~3 meteors hitting each target on average. Single target will damage potential probably go to the warrior, or more likely rogue, unless the target is super heavily armored, in which case death punch mage will win).
With proper build you can probably solo any encounter mid game forward, be it mage, rogue, ranger or warrior, not using any stupid immortality setups as well. I'm sure soloing the whole game is also possible, although I haven't tried it, and it might require some of the more optimal builds.
You also don't need to stay "pure", since there's a lot to gain from abilities of other classes, and you don't need more than 15 STR with gear (+6 is quite easy to get on items/enchants which don't overlap with any other potentially useful stat bonuses). The only use for more STR is to carry 1000 pound chest and drop it on enemies which is broken too to be fair.
The biggest problem I see as melee is early game, where it takes most of your AP to even get to enemy lines. Rushing blacksmithing 2 to remove movement penalty on armor might help. Melee is also kinda boring because you only get a few abilities and you don't get to use them very often.
Overall I would say that melee is not terrible and discussing which broken build is more broken right now is kinda pointless (Although the most broken build atm is probably a TK build ).
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