Currently, there is a very small delta between your DPS while standing still and DPS while moving.
Here’s a random section of a random Iron Juggernaut log during a part of the fight where movement generally isn’t happening.
Lightning Bolt accounts for 47.5% of the damage being dealt in this stretch of time, which is roughly 40 seconds long. 38% from Lightning Bolt directly, 7% from Fulmination, and presumably about 2.5% from Multistrike. If you’re moving for this entire duration and happen to lose ALL of that Lightning Bolt generated damage, you’re going to be doing 52.5% of your stationary DPS.
Lava Burst is also affected, so all Lava Burst casts that weren’t cast under the effects of Lava Surge are also removed, which is 29% of your Lava Burst damage lost, or a total of 56.5% of your overall damage lost during movement.
Doing only 43.5% of your damage during movement seems like it might kinda suck… but that’s ignoring an awful lot.
Since this is a period of 40 seconds, a Shaman with glyphed Spiritwalker’s Grace can cast-while-moving for exactly half that duration, reducing the damage loss to 28.25%. Still pretty significant, but now you’re doing over 70% of your standstill DPS. Because Earth Shock isn’t pressed on cooldown during movement, you can also add that in a bit more often than it’s being cast in this segment for when Spiritwalker’s Grace isn’t up. This would increase Earth Shock cast frequency by 100% for 50% of the time, resulting in two additional casts for .75% additional damage, and you can refresh Searing Totem so you don’t need to interrupt your rotation to do it later.
Post Lightning Bolt nerf, damage would be reduced by 27.5% in the above sample.
Currently, damage would be reduced by about 6% in the above sample.
Being able to do 72.5% of your normal DPS during a 40 second window of steady movement is pretty damn good.
It’s not at all like early Cataclysm where Elemental didn’t have instant Lava Bursts from Lava Surge and would suffer much larger DPS losses during heavy movement. Rarely does an encounter even now expect you to move for that long, and the short movement periods you are frequently asked to make are more easily covered with instant cast spells.
Nearly every other ranged DPS already has a larger penalty than that for movement, and nearly all of them are also getting nerfed by similar degrees.