Anyone saying the Avvar is weak hasn't played him enough! He just plays differently than the other warriors. He has two good abilities for generating guard, and an ability that functions like a mobile static cage. Most of his abilities have decently fast cooldowns as well. He's nowhere near the tank the legionaire is but he's on par with the Katari tank-wise if you spec and play him right.
I've played him quite a bit with my gear, but without most of my stats. He's still paper-thin. I can absolutely dominate threatening, but only with extreme end-game gear. I suspect I can start to do better in Perilous, but that's due to promotes allowing the crit abilities to actually function, rather than the kit being inherently balanced.
He's certainly NOT on par with the Katari Tank wise. Katari are a living wrecking ball of doom with 2k+ health, guard on hit, and knockdown / stun on half 3/4th his moves. Avvar does not stagger, and only sometimes shocks/freezes. He does chill. His Crushing Leap is also... ugh. I really love his Lady's Wrath, but it will not be nearly as effective as the enemy health scales up.