DCUO and AOC faile dbecause both relied not on player skill, but on LEVELS and GEAR.
If you want player skill in combat to make a difference, you have to allow it now, and not make gear/lv's > every little thing or you can get around it by having tier systems.
That's one thing Warhammer did excellent. In PVPthe lower lv's got buffed to higher lv's in pvp area's, and it worked great. You could pvp whenever you wanted and didn't hav eto race to lv to do it.
AoC's big problem in PVP from a melee standpoint was being immobile casting a combo.