Whether my gear is red or blue should have no bearing on how well I can fulfill my role.
As far as I'm aware, wearing AF or not has no bearing on how well you can fulfill your role either. Since that isn't even the point of class-specific gear in the first place. And what you just said was something people weren't fine with. Sharing the same gear aesthetics with other classes rubbed people the wrong way.

It should not define me as a tank, it should define me as someone who likes the color red.
Like it or not, color defines classes as much as gear model does. Paladin has white armor. Red mage has red armor. Black mage has black armor. Dragoon has purple-ish armor. The color most certainly is a significant factor of defining- and distinguishing a class or a job.

Now we're supposed to just excuse it as magical and let the lore be destroyed?
Now we are bonding with our pants and then, we magically turn the pants into a colored gem. Let's not start going too deeply into that stuff or we just might blow their cover. Although I like your reasoning as well

the stat bonus comes from the addition of an item to the piece of equipment