Rapid Fire for MM is intended as a focus builder and there are VERY FEW cases where you find resource builders to also have high damage potential.
I would argue that it should be/and is the exact opposite. MM with it's more hard-hitting, instant damage-based abilities is/should be the short window-burst spec while ranged Survival would be the less bursty, consistent spec that builds up it's damage.
Why? I would say it fits the fantasy more this way. Standing still and lining up perfectly aimed shots(I couldn't resist...
), should mean that in short windows of time you could push out A LOT of damage before moving to another place.
If you're moving around all the time, not having perfect aim but at the same time, this wouldn't really matter anyway as your toxins/venoms and explosives would do the job for you as long as you hit your enemy. This would fit better with a more steady/consistent playstyle.
Again, this is entirely based on what we in our heads imagine actual Spec Fantasy to be.