[BLANKET FIX] Mobility creep
Lets face it mobility is out of control for nearly every champion who is in the or has been in the LCS pool. Its obvious that mobility is heavily preferred over strong CC because it allows for much more fluid positioning (I mean that the positioning is constantly changing), and makes landing skillshots much more difficult. I could go on about how LoL is a video game with a competitive pieces, it is not a sport. I could say the game should be built around what players want to play, not what looks pretty. Instead, I present a simple solution to sheer amounts of mobility in the form of dashes, and teleports:
MY SIMPLE SOLUTION:
All Summoner Spells, non-ultimate based abilities, Certain ultimates that provide an unnecessary amount of extra mobility and passives that provide mobility (mobility meaning short term, short range re-positioning) now incur a 1 second 30% slow after using said mobility effects. Abilities that that provide a constantly refreshing mobility such as 
's Ultimate and 
's passive and 
's E ability will add an additional 1 second to the movement speed reduction for each dash/teleport assuming the player does not allow the slow to tick off.
The Idea here is not to make mobility irrelevant, quite the contrary it has use and value, instead it is to add a downside that has to be considered when using said mobility. Yes even flash is affected by this; at the present The summoner spell  is one of the most used Summoner Spells in the game thus severely limiting player options and choices. The fact Flash is so strong makes it mandatory to deal with extremely mobile champions; if we do not include it will become even stronger. I would nerf Flash even more buy making it only teleport your champion forward in the direction your champion is facing, but I'd rather see what the initial change does first.
On the point I mentioned "*Certain ultimates that provide an unnecessary amount of extra mobility*", Its fine if you need to gap close to target to deal your damage like 's ultimate or 's ultimate, but if you're getting craploads of extra mobility from your ultimate like  (even with the mana cost getting more expensive) it becomes an issue because that mobility in a realistic fight is extra and thus needs to either be toned down if not outright removed. About  's by the way, the teleport that can be triggered after using it would incur the 30% slow, because that is extra.
Again, at the present we have a bunch of highly mobile ["Polymath"](https://en.wikipedia.org/wiki/Polymath) Champions in the LCS pool. I think what needs to happen is each champion needs to have a niche role with weaknesses. Pros seem to pick all around good champions, so Riot, you should be trying to shape these champions so they fit a single role or pay a "hybrid tax" that lets them do many things but none amazingly. Addressing mobility is a possible 1st step to achieving a more cohesive balance.
I understand, the Competitive environment is full of energy and draws crowds, BUT playing your game and watching it are two very different things. Please, I beg, do not sacrifice player enjoyment (They'll stop buying your skins) for the sake of being hyper competitive. I do believe what made this game initially popular in the competitive scene was the fact it is simple to learn but difficult to master. Trying to shove the competitive environment down the throats of your player-base not your spectators RAISES toxicity in ranked play and alienates long-time players; long-time players that if you keep them happy will stick around unlike those crowds of people.