The other "ranged" mobile class was due to a design flaw with how their spell worked, and that was with Balance Druids. (Running Moonfire spam, quick-cast Wrath, Root kiting.)
The current Caster classes have immense periods of burst that they can dish out to compensate with the removal of constant mobility. Hunter's have had several of their hard-hitting CD's removed since they are now a mobile ranged classes again. They still have burst CD's, but nothing on par to the Casters. Which adjusts for them to have a slightly higher sustained damage throughput.