A new Champion Idea I kinda thought about. I would like your opinion (good or bad)

What if there was a champion whose passive was to become immune to the first ability hit every 10-20 seconds. But he has crap AD and Ap scaling, but the highest starting and gaining Armor and MR. All his abilities where huge aoe stuns and slows. Kinda like Leona, but better like the ultimate tank. They made it practically impossible to do large amounts of damage from him, but he took crap loads before dying.

Melee Such as (Level 1 - Level 18) Health: 700-1700 Health Regen: 10-30 Mana: 300-750 Mana Regen: 6-15 Attack Damage: 20-70 Attack Speed: .4-.7 Armor: 50-100 Magic Resist: 35-55 Movement Speed: 335

Abilities: Passive: Becomes immune to first ability hit every 20/18/16/14 seconds (reduced by 1 second for every ability afterwards)

Mana: 50 Cooldown: 15 Range: 1600 Q: Throws something that stuns everyone in the middle for (1/1.2/1.4/1.6/1.8) seconds and outside slows (50%/55%/60%/65%70%) for 2 second and does 20/40/60/80/100 (.2 AP) magic damage. Ability hit range: 350 Middle range: 150

Mana:70 Cooldown:10/8.5/6/5.5/3 Range:500 W: He sends out some pulse in a cone in front of him that slows all enemies by (70%/72%/74%/76%/78%) for 1.5 seconds and deals (10/30/50/70/90) (.3 AP) Cone degree: 30

Mana:50 Cooldown:5/4.5/4/3.5/3 Range: Melee range E: He stuns the first enemy hit.

Mana:130/140/150 Cooldown:3 min Range:700 R: He deals (20%/30%/40%) of the damage taken in the last 3 second in magic damage to enemies around him.

I know it might be bad, but just tell me what you thing and it would be great if Riot could give me their opinion as well. I also want to know what you may change and what is op or underpowered.