SNACs are primarily for bombers to deal damage to cap ships. Landing one on a snub's hull will instakill it yes, but that's not easy to do, it's a high risk high reward exercise that seems to be is fine as it is.
If SNACs are to be changed in any way, that would actually have to increase their damage with maybe a decrease in efficiency or refire. The point of the SNAC is to dump the ship's core into burst damage against larger ships. This burst damage allows the much lighter snubs to get in and out of the range of the highly dangerous cap weaponry quickly. A higher refire, lower damage SNAC goes completely against the intent of the weapon as it would require longer periods spent in a position where the cap can annihilate the snub with ease.
Bomber energy cannons fill this purpose. I think their excellent dps and efficiency are often overlooked, but they of course require being close to a large ship for extended periods to expend the bomber's core and are not ideal for anti-cap work.