Actually Musahashi, I did notice the same. And I actually did have some numbers a while ago. When the new Mog thingy "Martial expert" or whatever it was called came out, which I believe makes it easier to level up skills, I tried to go and skill up my guard, i have it laying around 170ish so I went to some mobs that are considered EM, T+ to level up guard, and in 3 hours I didnt get 1 level up. I even PM'd a GM to ask him if there is a bug in the mog martial expert bonus, or if it doesnt affect defensive skills at all. He said he'll check with the DEV, and I never heard back, lol.
I love skilling up guard, its somehow fun, specially when you have nothing better to do.. but not getting 1 single level up for 3+ hours is just sad.