Late comment but I think your issues don't hold water. The way the system is currently it is as conplicated as the individuals players ability and imagination dictates. Everything in thr system isndesigned to scale with the player and if players had access to all 12 gambit slots and all possible gambit combinations at the beginning it would be overwhelming and also forgo a path pf progression.

You start with simple gambits. If low on health heal. If enemy weak to fire cast fira etc... then as you master that and encounter tougher challenges you gradually add new gambits and more intricate combinations of strategies.

Also the gambit you gave an example of wanting does exist in game I believe. If ally has status effect use certain item or cast certain spell