Since everyone has the 'nerf health' fallacy covered, I'll address the 'nerf CC' fallacy myself.
Elise has one stun in her kit, and it's a linear skillshot that only affects one target.
Renekton has one stun in his kit, and while I'll admit is the core of any balancing issues with him, that is because of the double or triple auto-proc on an ability that already acts as an auto reset, not because of the stun itself.
Malzahar has one channeled dsuppression as his ult, which means though you can't do anything, he can't either without canceling the ult early. He also has an AoE groundsource silence with Q.
Syndra has an AoE knockback as her only CC, and it requires her to rank it up five times to maximize its potential.
Jax has one AoE stun that, while good, is mostly so because it is one of the last dodge mechanics in the game.
Jarvan has one hard CC, and that's his EQ combo. The fact you use him as an example and not Azir who has QE as well as a knockback wall as his ult is kinda confusing, though maybe its the slow on his W.