Lets get some Mobility counters
If mobility is such an issue, why not implement so mobility counters? a few Examples, Dota 2's Bloodseeker, his ultmate is Rupture: "If the unit moves, it takes a percentage of the distance traveled as damage." also Ezalor with his mana leak; "Weakens an enemy's magical essence, causing them to lose mana as they move. If the enemy loses all of its mana, it will be stunned."
many players feel mobility is out of control. implementing mechanics like this (doesnt have to be exactly this) could help. it could even be on an item like the jungle items with challenging smite. you "challenge" a champ and if they run, they take damage etc. it would also indirectly buff all the "obsolete" immobile champs we never see.