While I personally love using dualist and scavenger (fine specializations btw) the others are lacking.
liberator is rendered completely useless the second the alarms are tripped which any decent pred would do.
Rush down requires AI for it to be of any use whereas an amphibious recon can do the same but better because all it requires is water which includes muddied areas and instantly muds you up as well.
Dualist is alright and makes the 1011-12 pretty damn good however its DPS is out matched by a recon with sniper or an assault/Dutch with deadly. All of those classes can take more of a beating and can bring gear to help the team or throw grenades for even more damage.
Scavenger I have no problems with. It’s a great specialization that helps with the weapon crate issues of them being nearly useless.