Giving him a Knock-Up on his E would probably break him, again. It'd make him even more reliable. The shield can be compensated for by playing more carefully. Meanwhile, his opponents would end up eating two stuns in a row followed by at least three hits from two soldiers, and it would come out at a speed that's virtually impossible to react to.
Azir needs a rework, a very large scale one, severely.
He's an early-game bully with hyper-carry scaling AoE damage, a wall that stops dashes, self-peel, a shield, the most flexible and arguably longest ranged dash in the game. He's extremely safe to play, and has extremely reliable strengths.
And this isn't just listing all the positives in his kit without listing negatives. That's listing the /outliers/ of his positives.
To be honest, he doesn't actually have many, if any, significant weaknesses.