So what advantage do mages get for wearing NO armor whatsoever, that's the question.
He answered this already. But let me break it down for you;
The way it works is you gain a level for every X number of skill increases. Lets assume you need 20 points to go up a level
Mage 1 skills (that are being used/focused on):
Destruction
Restoration
Alteration
Conjuration
Mage 2 skills (that are being used/focused on):
Destruction
Restoration
Alteration
Conjuration
Light Armor
Assuming roughly equal usage, Mage 1 will level when each skill is at 5, where as Mage 2 will level when each skill is at 4. Meaning at level 21, Mage 1 is maxed out on his 4 core skills, where as Mage 2 is still at 80 in each. Mage 1 becomes the more powerful mage, where as Mage 2 is more utilitarian, but less powerful with the magics.
Also, skill level will affect which perks we can take, so in my example, Mage 1 will have access to higher level perks than Mage 2.