I thought the gambits were a good way to be able to set the boring, repetitive things you always do in battle to automatic and not worry about them. Certainly stream lined the fights a little, but like you said, hardly necessary. With enough fine tuning though, you could really make everything work automatically and perfectly. The system was flexible but not essential, so if you were rubbish at it, you weren't going to throw the game down in frustration. I like that Square Enix tried something new and I feel like it was a fairly moderate success, tbh.