Though I agree on the rotation side of things (doesn't yet feel that good and not going through 1-2-3 means we miss out on shield & heal), 2 cartridge only wouldn't mean a qol change for me. Might be a change in regards to preferred gameplay for some, but that's it pretty much.

On the constructive side of things, there might be some things that could work actually. Remove 20% damage buff and put it into double down. On hit, double down restores one bullet.

Now what would change? In the end, we would now always start burst with double down. We would always need 2 cartridges min to start the phase, but even after initiation with double down, there is both burst skills available to chain into. Those changes would make for a easier rotation and way more obvious best rotation that can be followed and improvised even when things go south in between.

We would have only lost a button that serves only to buff percentage. I hate all skills that just do some change to stats. I want skills feel reactive, not mere stat or percentage boosts - boring! But that might just be me.

In regards to "perfect balance": I don't think gunbreaker would be overperforming with this change. I actually would suppose a slight buff to gnashing fang, in that the finisher grants 200 shield / heal as well. That is due to the fact that we are going thorugh 1-2-3 only "rarely", so having a small potency shield / heal every 30 seconds would really feel as if something helpful is prinkled in there. I think overall, all those changes would bring gunbreaker into what might be the "perfect spot" for this expansion. Not saying it couldn't be better, but even what I do propose - sadly to me - is way more then we likely will see.