TL;DR version[/B] : You are correct, mercs are poorly developed and i see no future for the class in pvp, at all.
Yet it's more important for BW to "fix" a "broken AC" like Shadow/Sins to give them 3 fully viable tree like Marauder along with multiple fully rWZ capable hybrid spec (shadowsins were actually the best node defender in the entire game even before 1.4 hence they are wanted in rWZ).
As well making the warrior's shared tree super powerful and newbie baddie proof to play.
It's just BW's way of balancing. They want to buff the best classes 1st to "complete" it the underpowered / unwanted / extinct crappy AC/Spec just gotta have to wait. They are afraid they will piss off the fotm kids and lose more subs.