I didn't mean to detract from your original point, because I think your intension was in the right place. Most classes do have spells or abilities they can cast on the fly, or things that are near instant they can pause very briefly to throw at the mob. Hunters should definitely be using Arcane Shot while moving, and I like using Multi-shot the second I stop since it's a .5s cast that gets damage going back on the mob a lot more quickly than steady shot. Those are just a few things Hunters can do to bring up damage and DPS time, I'll leave what other classes can do to people with more experience on them.

I know it isn't specifically a lurker thread but you can increase your dps time by not backing out for whirls and instead going forward into the water. He will whirl and knock you right back to the spot you would be normally dpsing from losing no dps time in the process.

If you know where to move ahead of time you can move while casting your instants. Al'ar P1 is a good example.