I explained it like this:

Imagine you are in raid, and you are learning and haven't cleared yet, you have no need for cleric stance, and some abilities are not necessary all the time (such as esuna). When you clear however, you then switch cleric stance in and switch out something like eye for an eye which you no longer need.

The point is that this system allows players to think about their toolkit, and adjust it situationally. Yes, all of these abilities are important, but by limiting you it allows you to prioritise the ones that are truly important in that singular encounter, and gain a new understanding of how your class plays in different scenarios.

I'm wondering if this will bring a new age in which not using protect is a viable strategy (probably not)