When it comes to mages, I would say a ward is a terrible means to defend against arrows. When it comes to magical barriers to block physical strikes, I always imagined a ward dissipating the kinetic energy over the entire surface of the 'bubble'. A single, high-velocity strike in a single, small point would be an intense amount of force in a very small area to actually dissipate.
I'm not saying it couldn'tcouldn't block it, but it would likely expend a HUGE amount of magika in the process. And if it was a rain of arrows army style? Mage-bane.
Then again, there are always other defenses, such as raising up a wall of stone or ice to block them. Or if a mage if feeling ballzy and wants to show off, a ward laced with a disintegrate weapon spell to help soften the blows on their barrier.
Just my thoughts though, I love threads like this XD