The fact that willpower increases when you're committed and decreases when you're less motivated... makes it not feel like a status (or power)... makes it feel more like a condition or "level of motivation"
will power will be an interesting thing to quantify later in the story I imagine, since itll constantly have small or large fluctuations in different states of mind
the fact that willpower could increase and decrease is pretty realistic. we all lose the motivation to continue sometimes and want to just give up once in a while, pretty nice detail.