So a starting Character starts with 2 Hits.
Wearing armour can give you 4 Hits for Free, as well as protecting you from Cleave/Impale (and remember Impale is called on all arrows.)
To get half that protection, the Mage needs to spend 2 XP and is still vulnerable to all those calls.
As a Mage this discrepancy is enough that I when I took to the field in armour, because with reasonable hard skills I could be useful with no Calls at all, I did not find that as a Mage.
Bear in mind that many mage spells are 2 Mana to cast: Shatter, Paralyse – These are in a similar take the enemy out of the fight range as Cleave and Impale. The Offensive 1 mana Mage spells don’t tend to do this, and in the case of Venom and Weakness are the only two calls that you expend mana.
Finally Empower is a 2 mana spell, it essentially replicates a 1 HP ability.