Azir's release kit, like many recent champions such as Kalista and Tahm Kench, was seriously overloaded. They had no choice but to gut Azir. It would have been fine if they had left his mobility and just nerfed his damage. But instead they did both. Now he sucks.
Notable successes imo include Jhin and reworked Poppy. All they needed were some tweaks. Their kits are simple and straight-forward. Easy to understand. They don't have 15 passives. They do what they are supposed to do. Nothing more. Nothing less.
Lee Sin's problem is that he is so flexible that he can petty much do anything. His skill floor is basement low and his skill ceiling is astronomical. In the hands of a practiced player he is god-like. In the hands of a scrub he is still viable because he can go full tank and still have all the shields and mobility in the world. Meanwhile, Braum still can't ward jump.
His biggest problem is that at his core he is a displacement / mobility champ with a massively over-loaded kit. He has all the advantages of an assassin (mobility+high burst) but none of the drawbacks (not squishy).
Lee could be instantly fixed if Riot would gut his damage and instead focus him on CC, mobility, and displacement abilities. Then he could do things like jump in, kick, stun, slide around, whatever, and then just swag-walk out like he does now. He would still be Lee Sin. But he wouldn't be friggin Kenshiro, Raoh, and Sagat all at the same time.