Ok, listen, i love this game, but i can't stand the fact that when in a fight, changing menus gives the enemy a free hit. That doesn't make any sense and i hate it.
And the concept of a "stance change" requiring an action isn't exactly unique. I vaguely remember even Final Fantasy playing with the mechanic is one or two of their games.Maybe read the battle log. Picking the items button makes you open your bag, which is an action. Incantation is basically chanting for a stronger spell (it is why the cheapest spells are in the standard "balanced" stance). Shifting to a defensive stance for further defenses is an action the enemy can see you do. Every choices has meaning. Think of it as you and the enemy taking actions simultaneously, rather than going back and forth. Agility may let you act first, but perception lets you see their next action, which helps you plan ahead (if your attack can't interrupt their next attack, switching to defenses may let you wait as they get themselves unbalanced or tired; the opposite is true, and so on). I know this game is very unusual compared to other turn-based combat titles, but it makes sense the more you spend time with the game.
You're not simply "changing menus." You're switching your stance. It requires you to actively consider whether you're better off staying in the stance you're in and using a less effective move or lose a turn in favor of selecting the move you actually want next turn.
Also, certain moves change your stance automatically so just use the appropriate one.