Railguneer
This is an underused nanofiber'd infantry honestly. Either the player's busy fibering different troops or they just ignore Lancers in late-game sometimes (especially Last Bastion users).
Duplicant
One of the more underused infantry units really. Same as what I said about Railguneers, except Duplicants are almost non-existent.
Synchronin and Synchronaut
Underused, especially the nanofiber'd ones.
Deviatress
I do see Huntresses, but really never their nano'd forms. Probably almost non-existent, but I'd probably at least see em more over Duplicants.
Zorbtrotter and Zorbfloater
Easily overused for how effective they are at busting infantry groups, especially the nano'd form. Honestly gonna say they may need a nerf, especially the Floater's healing speed.
GiantsBane and GodsBane
Let's face it. They're overused especially the Godsbanes. I can't really find a way to counter a large group of these guys without Iron Curtained Terror Drones. Perhaps they, especially the Godsbanes, need a nerf somehow, or more noticeable counters.
SODAR Array
Very underused, even when counting the few that are around bases. I really never see one accompanying an attack force either. You think there's a way for it to be improved to encourage using it or will the players just miss out?
Pteranodon
Definitely overused. It's actually to the point where some players may even spam these to attack bases after they bust through armor divisions and miners. I do think a nerf is in order for em somehow, but not sure how. It's between their huge HP or their ability to fire on the move, or simply their speed I'd say. I know infantry/base defenses counter em, but Soviets probably have the worst time, honorable mention to Epsilon and their Gatling Cannons doing little to nothing against them.
Tarchia
Underused. Most Coronia prefer the flying bombers over these things. That's it really.
Eureka
Underused. Can cause friendly fire, doesn't often catch the units, and is generally only anti-armor, and as someone said before, Pteranodons do the job better.
Diverbee
Underused. Most Haihead players I come across prefer to mass Megalodons and ignore Diverbees.
Megalodon
Overused. Powerful, especially with the arena power that helps em bust through mass infantry, while making em very bulky too.
Turmoil Grid
I specifically said this one instead of Stun Grid because some players actually do use Stun ones, but mostly to just keep spies away from their Cloud Piercer.
Reprocessor
No explanation needed on it being overused except that it needs nerfs.
Blast Furnace
Very underused. I would guess most maps that don't have flat surfaces make it hard for this SW to be used really well and even then, little to no person builds it in the first place.
Knightfall
You'd think that from many of the Coronia players that I see some of em would at least use this. Most don't, and thus underused.
Signal Jammer
I think this is really non-existent as an ability. Underused.
Quetzal Shield
Surprised I don't see Coronia players use this. Underused.