honestly, i don't see a problem with this. big ships are currently massively underpowered compared to things like double chaff vipers and cobras.
it would make sense to me that a gun which costs more than the combined insurance and module cost of your target's ENTIRE SHIP should be capable of inflicting massive, lethal damage... perhaps not a one-shot-kill, but enough to inflict serious hull damage and bypass shields with one shot.
anyone whose flown a bigger ship against double chaffed smaller ships knows that the current weapon selection does NOT appropriately reward the player for the incredible amount of skill it takes to aim manual weapons at smaller ships without any aim assist at all.