A typical arcane spec (53/18/0 or so) has 17 points on effective DPS talents (at least 1% DPS/point), the rest are subpar, fillers or utility.
A typical fire spec (0/51/20) has 44 points spent on effective DPS talents.
Shitty trees produce shitty DPS, it's just that simple.
The only thing that makes arcane viable is a seemingly randomly given inherent +75% DPS bonus for one spell.
Dude, no need to call Arcane out. You play your fire style and Arcane mages will play theirs. In my opinion Fire and Frost are shitty trees, but I don't go around claiming that as a fact. Arcane isn't a "shitty" tree. Sure it's different from the style of fire, but it isn't shitty.