Support Character

Ahem, more seriously, Staff+Shield is the most natural way to Support. Here are my arguments.
1. Buff to Bless: It also uses your MATK for its healing value when you equip a staff.
2. Reverse proration master: Besides Impact (because everyone uses it) and Punish Ray, Staffs and MD are the only weapons that use Magic skills, not because the others can't, but because they are more suited for this. Also, they get access to Power Wave with buffs instead of nerfs, unlike other classes. More specifically, Staff gets an even bigger distance than every other weapon as well as a 40% damage increase. Since everyone else uses physical skills, having proration for them is important.
3. Quick MP Charge: I can't stress this enough. This makes supporting waaaaaay easier.
4. You CAN go for DPS: If you don't mind losing some damage or auras (because screw auras), you can invest in INT then DEX and take damaging spells as well as healing/supporting spells. You lose a bit in cast time, but overall you become a class that can do two jobs and can fit multiple situations. You're even tanky in some of them.

 

I see where your coming from, seriously. But all I've said in my comment were solely based on my experience, as a support I focused my skills not heavily on proration and damage, I wanted to be able to let my teammates survive. To do that I maintain buffs basically whilst keeping aggro low. I don't really want to explain the obvious mechanics like aggro control through skill sneak, high aggro combos, QuickDraw mechanics, guard mechanics etc. True doe staff/shield - feels naturally a support class, it's easy to get items for them too

 

Yeah, I understand where you come from as well. I'm also speaking with my own experience and knowledge of the matter.
My mage's role is not only to be a support, but also an attacker. Thus it has multiple jobs it can fill and be useful in more ways than one (who needs support if you have Revs, but DPS are always welcome).
However, I do recognize the advantages of being a Bowgun/Shield. You have DEX as your main stat, which increases your cast rate significantly. You have also a naturally long range, allowing you to keep yourself safe.