How about scratching the HP buff from T2 list and in stead give them a research that:
A) improves their silly range
B) either makes them more durable OR makes them faster (It's T2 with the alternative of scourges, they can be even faster and still not broken by then)
C) upgrade their terrorfex to deal more morale dmg or have an aoe
... or pretty much ANYTHING aside from hp buff wich isn't as useful in their case as many other things would be.
Even such a thing as +10 range would work wonders, to hell with increased hp!