Agreed, Yeah there was an issue is that the two specs had a portion of abilities that were shared between each other but that could've been fixed by separating them and putting them in the spec that ability was suited for.
Arcane Shot never made sense for MM just like Cobra and Kill Shot never made sense for SV. MM should've been a spec that focus on casting while SV was a run and gun spec that had no cd.
I think I recall when Fury could use Colossus Smash but they decided that it should've been only usable as Arms. That's what Blizz should've did with the abilities between MM and SV.