Yes, Onatel will be a much more consistent tank than Azlar.
Azlar is high risk high reward. If opponent color stacks 3+ blues and gets an okay board Azlar will die before even casting his special. So he’s a bad tank in some ways because of that. However if the opponent doesn’t color stack, makes a mistake or has a bad board Azlar’s special may singlehandedly win you the match. So he’s punishing when he goes off but melts like butter too often.
Onatel is much tankier, much more survivable. She’ll on average survive longer than Azlar so it buys you time for your other heroes to make a difference. Her special can be punishing if people don’t play around it well.
Once Onatel is maxed I think a defense of
would be your best bet IMO. Purple flanks go great with a yellow tank. It’s hard to color stack VS that team effectively. I prefer fast or very fast characters on the outside.