... is not that its "too powerful".
... is not that its "too long ranged".
... is not that its "too unbalancing".
... so forth and so on....
... no, the real problem with ECM is the ships that use it.
They have extra mid slots so that they can fit ECM AND shield tank, but no sane ECM pilot bothers with that. At most, they might fit armour mods in the lows like on a Scorpion. If they somehow capped the number of ECM mods that could be fitted (3 for frigate, 4 for cruiser, 5 for battleship as opposed to 5, 6-7, and 8) then suddenly the supposedly overpowered ECM ships are not so hot. Still useful, and still have numerous whiners complain about them, but not as many I bet.
So how to accomplish such a cap? Simply reducing the number of mid slots makes the ships too weak. I suggest either coding a cap much like you can only fit 1 AB or MWD on a ship now; it will encourage players to use the other mid slots like they were intended: propulsion, shield tanks, sensor boosters, etc.
The reason I post this is because I believe simply by gaguing the amount of whines on the forums that sooner or later Falcons and their ilk (but especially Falcons) will be toned down. I admit that the way they are becoming the go-to Recon ship beyond all others suggests some balancing is required. Sigh.