Speed - The Forgotten Problem...
Everyone always talks about champions or items being overpowered but to me, that is not the main problem with the game. I do not see damage as an issue but I think that speed is.
Everything gives champions speed that they were originally not designed to have, from runes to items and it turns champions from balanced on paper, to unbreakable messes.
I simply do not want to be hyperactive to play this game. I feel that reaction time is getting shorter and shorter each season because Riot seem to want snowball champions to be dominant. I personally do not feel that any method of play should be dominating and (mostly AD) champions have access to too many speed boosts these days, which makes it too easy to avoid skill-shots.
Slowing the game down would be the optimal solution, getting rid of some of the excess speed that certain champions have. Since if they already have a speed boost in their kit, why would they need another one?
If you MISS a SNARE, you do not get another one, so why would you get to try again with another speed boost?
while older champs were also at one point balanced around champs dodging their spells 
, however that was toxic so they nerfed/reworked those champions.
I mean think of old Morgana, now look at new 
, what was it that made her pick or ban after her rework.... her SPEED.
That being said, most champs are balanced nowadays around DODGING skillshots, but if 1 ever hits(the cc ones) thats 99 more skill shots that are gonna hit the stationary target instantly deleting them. Short garunteed cc 
makes it impossible to "dodge" the really long easy to dodge hard cc 
that results in your champ being stationary and dead to the 5 other abilities that hit them immediately after.
This is why champs like yasuo arent broken, 
can W yasuo and then morg his the qw on him while he is temporarily unable to use windwall.
This however makes champs like 
INCREDIBLY vulnerable since they will hav ea much harder time dodging the cc as opposed to yasuos windwall, this leads to them being COMPLETELY OVERSTATED in their effective range, reading the 3 paragraph nasus R, and still seeing him sub or at 50% winrate leaves you questioning how broken everything else is in this game.