GNB QoL Change:

[Ixon]

Double Down should stay at 2 cartrigdes, its an important part of the ability lore/fantasy, an easy "fix" could be to increase the cd to 120 and increase potencys of other skills so you need less cartridges per minute

"Double Down" in FFXIV is taken from Seifers Limit Break in Final fantasy 8 called... Bloodfest: https://www.youtube.com/watch?v=Lb86P49jb1Q

It's obvious that SE took inspiration from both Squal and Seifer's move sets in FF8, but then took liberty when naming them and updating their animation. I do not think there is anything lore related about cartridges at all, so SE is at liberty to do whatever they want.