Well, if chaingun have such pin-point accuracy in small bursts now, why not give a 4x or 6x zoom for it?
Because, frankly, anything short of a sniper rifle fielding more then 4x optics (and that's towards the most accurate of accurate guns, too, mind you) is pointless and ridiculous. But then the jackhammer can have high optics too, so why the hell not.
Eh, some of the LMGs do great with 6x optics. You can pop your shield, eat a headshot, and completely wreck snipers at what they think is sniper-only distance in a fraction of a second. (Though, to be fair, if you've got a steady hand you can do the same thing with 4x or even 2x optics.)