At 1 heat per shot and 2 shots per second, the AC/2 generates 2 heat per second. That's more than any weapon in the game short of the heaviest energy weapons, and much more than the AC/5's 0.59 heat per second. The entire schtick of ballistic weapons is that they're heavy and ammo-dependent in exchange for relatively low-heat damage, and this problem runs against the grain of that and makes the AC/2 not particularly viable.
The heat generation of the AC/2 can probably be halved with no other changes to the weapon. Personally, I'd go further and cut it to a third, but slow the firing rate to 0.75 shots per second, which would drop the heat per second below that of the AC/5 without buffing the weapon too much.
edit: Just imagine when the Jagermech is introduced, and new players are given it as a trial 'mech with single heat sinks. It'll be worse than the stock Dragon -5N.
Edited by kiltymonroe, 24 February 2013 - 12:13 PM.