So today I tested this with a sharpness 5 diamond sword against tier 3 protection 5 power armor and protection 4 diamond armor. Even though tier 3 armor supposedly has more armor points and I have more protection levels on it, I took 2 hearts from one hit from the sword. In protection 4 diamond armor I took 1 heart from the sword. Clearly, either the protection modifier or power armor in general is not acting as it should.
Unfortuantly, there is a sponge bug that prevents the custom armor attributes on power armor from working properly. There is not much I can do to fix this.
So today I tested this with a sharpness 5 diamond sword against tier 3 protection 5 power armor and protection 4 diamond armor. Even though tier 3 armor supposedly has more armor points and I have more protection levels on it, I took 2 hearts from one hit from the sword. In protection 4 diamond armor I took 1 heart from the sword. Clearly, either the protection modifier or power armor in general is not acting as it should.