but he just lacks the defensive capabilities of the Katari, and the inability to regen health like the Reaver.
Katari has high hp, guard on hit, mobility, knockdown, and occasional stun / fear. Reaver has heal on hit, fear, and occasional knockdown, alongside some mobility.
Avvar has Elemental, some stagger, but the ability to continually AoE attack (through cover) above and beyond what Reaver and Katari can, and with different elemental damage & effects.
I've recently soloed Perilous with the Avvar vs Venatori Commander on frost map. The lack of innate useful defenses were made up through high promotes and end game gear damage + heal on kill. He can kill multitudes of enemies very very quickly with the right setup, and by using ambush tactics.
Cover remains your best friend.
Lore implication: Skywatcher is a mage?
Yep, BW mentioned that in the twitch stream. Something about because he's an Avvar and because he volunteered to join the inquisition, he's outside of Templar / Chantry control, otherwise they'd consider him a mage.
Really he's the Elemental side of what DAO would consider Arcane Warrior. He's an "Elemental Warrior". DAI's AW is the spirit side.