Why, whenever Jax and Kayle are good, they are oppressive?

Jax does ridiculous burst damage, has mobility and hard cc, gets tank stats for building damage, and can build just about anything because lol hybrids.

Kayle is just too safe with too much damage at range and has a couple of the same problems as Jax.

Also mixed damage is an absolute bitch to balance.

Jax is a huge pile of free stats and needs a rework.... since he is nothing but a ball of stats there is really no way to tune him beyond'make him oppresive or crap' and it's incredibly snowbally in game. Rito plz give jax a new ultimate and passive kty

Usually the reason behind it is the inherent brokenness of a kit that can't be fixed with numbers, but with specific champions, I'm not sure,

For example: If a champion could do a Karthus ult for free every time he got a super complicated math question correct, that would be broken no matter what as the counterplay is small, it relies solely on the player and not the opponent, and even at minimal damage it would pop everyone's Banshee's so good luck surviving a Fizz + Karthus + EvilMathGenius comp where they bait Zhonya's and banshee's out then stomp the enemy.

Bad designs with low counterplay.

Cause these are archaic champion designs and basicaly have low to no incoming riot buzzword counterplay.