Maybe soon there will be only 3 or each unit class with minor changes, and no access to the other when you pick one. Each one would look different, for example, advanced aliens that use their minds, humans, and aliens that infest areas.
/trolling
On topic, I think that Banisher was useless with it's low DPS and high cost. With almost any micro at all, 2 or 3 raiders could easily kill it.