I don't know, its quite weak and the only thing it's useful for is harassing enemy engineers early game. Plus it can't hit moving units for their life. I don't see why its a problem.
They did, as they are in PA. TA had decent land scouts though. The reason for this is that they invalidate other scouts and prevent early expansion if they have a weapon. Someone has stingers guarding a fabber? That's cool, kill their unguarded fabber. Move their stingers to assist? Cool, kill the now undefended fabber. They do little but force air first. What gameplay reason is there to have fireflies be able to shoot?
Wait but if they have a stinger, how would you be able to kill the engineer? Stingers would kill the Firefly before it could do anything.
No real need for this. It is already so weak a fabber can build an AA turret before the scout can kill it.
Vision range of a firefly is greater than weapon range of a stinger. They can avoid the stingers easily. Not really true. It takes ~17 seconds for a firefly to kill a fabber. It takes 30 seconds for a fabber to build an AA gun.
Then the weapon range should be reduced to at least be equal to the stinger. Then if you leave your engies undefended it's your fault that a Firefly (or any other unit) got a cheap kill.