Maybe just maybe the fact that they get killed very, VERY easily is being overlooked. Of course they kill tanks. However, just as easily as they kills tanks... hornets kill them. If you have your AA countered then the gremlins will get worked.
What I feel made them OP was having gauss protecting them.
Gremlins > Tanks Hornets > gremlins Gauss > Hornets/ hawks then gremlins > all with hog protection
"hogs are totally op - playing terminal moraine 1v1 (i think thats the map - the one with the gun in the middle, snowy but not chasms)"