I feel like the armor is only for aesthetics and making separate categories for looting/crafting purposes. I just do not perceive a practical difference.
the armor classification differ in the armor value it provides, not just looting/crafting.
I believe it's about defining "silhouettes" for the different classes of profession they established. A lot of RPGs are very invested in a "warriors wear plate, wizards wear robes" mentality, GW2 challenged a lot of these, but preserving standard fantasy archetypes seems to have been something important to them. I think it helps provide the professions with identity, as well as clue people in to who or what they're looking at and what to expect from that character.
From that perspective, I very much miss the profession specific armor of GW1.
I believe armor in GW1 was more logical, the AL60 provide extra energy which makes the scholar class relay more on spells, AL70 provide extra versatile feature, AL80 provide the highest possible armor.
it is no the case in GW2, the armor class only differ in the armor value and there is no compensation for the loss of armor.