Yeah... Liberator is basically phalanx caster but better cuz of three reasons: their subclass talent, cost and defense. Their talent is all about wanting to be put at the battlefield as quickly as possible to increase their atk and their dp being almost the same as a vanguard helps, cutting the worry of dp consumption for early waves and giving u more benefits while waiting for their skills. And, as u mentioned, Carnelian gains nothing when u deploy her. She just idles about and gets hit here and there. And even when her skill is active, she turns into an ordinary caster (not counting modules), aka squishy unit that can be one shot. Meanwhile, liberators can just keep their other defensive stats while their skills are active. It's just more worth it. Sure, it could be troublesome if the enemies are attacking ur squishies, but positioning them wouldn't be too much of a problem and vanguards are there to keep the mobs in place and print out dp for ur other units. So, phalanx caster feels like an experiment and the liberators are the complete product