The problem is that there's a lot of stuff to interrupt casters from doing dmg.
And there are still very mobile speccs out there.
Sprint, killing spree, bladestorm, counterspell, wind sheer, stealth, vanish, blind, wyvern sting, death coil, shadowfury, shattering throw... You can also use all of this. Most melee speccs also have a slow build in theire build. Just play around with these spells and don't forgot to use divine shield ;).
Knochbacks for casters shares cooldown in answer for the charge change. So only 1 out of typhoon, thunderstorm and blast wave.