The game is beatable without perfectly timing your guards if you don't spend too much Power during attack turns, but I definitely could've made un-timed guards a lot less expensive.
I really wanted to focus on the tension that comes from managing that meter, making the choice to either spend more for a more reliable defense or risk it all for the reward of perfect guards in the middle of a difficult fight, but balancing that while taking into account players of varying skill levels was a real challenge.
The original plan also included skills that you could use outside of action turns, spending Power for uncontested damage or support effects, and a second party member who specialized more in that sort of thing. I wish I'd had the time to include that!