I'm liking Endwalker GNB more than Shadowbringers now that I've gotten used to it. My main complaints are that that moving bosses still feels pretty bad because of continuation. And that dying at all seems like a pretty severe upset to your rotation that you can never really recover from.

As for making double down cost one cartidge - I don't like that idea. Costing two cartridges seems pretty central to the identity of the ability, I'd prefer SE balance around that instead of taking away what makes it unique.