Wait a minute....what's wrong with the Short Circuit?
It's definitely not a weapon of killing, as it's more oriented towards support.
If I'm an engie, I definitely like to camp near my sentries. And if demos and soldiers get too close, I could be done for.
With a short circuit, I can effectively wipe out a sticky bomb carpet, rather than blowing up instantenously. I don't need to use my shotgun to blow them away or rely on a pyro to airblast them.
And I can do it constantly as long as I have a dispenser.