I'm tired of seeing so much 
.
Let's add some variety here.
My suggestion: "earthbound"
Earthbound targets an enemy champion, slowing them by 25% and grounds them by 2.5s
Effect can be removed by 
Cooldown: 180s Range: 650
Discuss!
Not very distinct from 
.
Having a grounding isn't enough to make up for the loss of the 40% damage reduction and 5% less MS reduction.
Also, no. Universal grounding is not the answer to mobility any more than universal GW is the answer to healing. GW has resulted in healing being buffed to where it's OP if the enemy has no GW, but still isn't relevant if they do have it. Making grounding readily available would just result in mobility getting the same treatment.
So it's like Exhaust but instead of reducing the damage you take from the target, you inhibit their Mobility instead. Would be a pretty good Summoner to take if you had to go up against a champion who can jump all over the place, For example, I can definitely see a Support taking this if the enemy team has an ADC with a Mobility spell like Lucian or Ezreal.
I don't know about this exact implementation, but a grounding summoner would probably be a great idea
2,5 second root is waaaayy too strong in comparison to other summoners.
