The problem isn't in the Mechanics. Looking at GW2 mechanics compared to other games such as WoW or GW1 and GW2 clearly has superior mechanics. The problem isn't with combat itself, the problem is with what's available for combat.
Looking back at GW1 we had 1000+ skills, absurd number, but it allowed for players to pick specific roles to fill. You had 8 slots and 2 professions to pick from. Players were able to play around in the sandbox, learn how they wanted to play, and tweak builds to suit the roles they wanted to fulfill.
Guild Wars 2 is very different due to the entire build revolving around your active weapon set. Combat also suffers from a lack of flexibility in expanding and contracting what specializations players have, but that's a much smaller issue. Build diversity is the real issue, and the game suffers from it because of the weapon centric system in place. There's just not enough flexibility.