I've heard many people criticize the game's gambit system. Why? The gambit system is amazing. It can help relieve repetitiveness so much. Because the game "plays itself"? Hardly. I don't care how good you are at setting up your gambits, there is no way you can program it to think of every situation that would arise. Besides, it's kind of like playing a football simulator in a way. Much of FFXII's challenge comes from setting up your party for upcoming situations, so in this regard setting up gambits would be akin picking a play before each down in Madden. It still requires player interaction for situations that are unpredictable. The Zodiac Job System version makes the gambit system even better by allowing players access to every gambit at the beginning of the game, making the system even more useful.
My main problem with the gambit system is that its customization is time consuming and the lack of gambit profiles. If I change the gambits to suit the enemy I'm currently fighting, I have to overwrite/delete the previous gambit settings. That results in me just not doing any changes at all even though in some areas depending on the enemy you would like to switch between two sets of gambits.
Also, even simple gambits will get you through the game and there is no need to ever manually use magic or items unless to cure a vicious status aflictions (mostly virus really). I think you can even make gambits for that.
If you play it conveniently, all you'll ever do is move your party around. Then it plays itself.
Also, as you pointed out character position hardly plays a role at all. Maybe because a gambit system that would incorporate AI for positioning would have been very complicated? My problem is, they made an unnecessarily complex system (Do I really need to choose the exact percentage of HP at which my character should heal? How does it really differ from "concentrate on healing", "concentrate on offense", "fight balancedly"?) and then they made the game far too easy because they knew their mainstream audience would struggle otherwise.
I much prefer FFXIII's paradigm system. Simple to use but deep in application, and that game has challenging battles in abundance in the main quest.
Story in XII was good, just not as good as you'd expect from Matsuno. Soundtrack was great, setting was too, I really only disliked the overly simple battles resulting from an unnecessarily complex gambit system.
And, yes people told me that the optional enemies require strategy beyond the simple 3 to 4 gambits that will bring you through the rest of the game. Doesn't make the main quest anymore interesting gameplay wise though.