how long does it change the size of a model? Seems like you only have to change a few numbers around, meaning the entire issue could be solved with a day of attention
On the surface it seems like it might be simple, but it actually has potential impact on lots of other things. One has to do with animation, as you scale up or down a character that will change the distance each given step will cover across the ground. The actual speed the champion moves does not change though. When these two things are really out of sync you get a foot sliding effect. Basically it will seem like the character is on ice skates. Trust me, animators hate that
One of the other reasons has to do with game play. If the scale of the character art does not match his hitbox (invisible box that registers a hit or miss when you click) you get lots of problems where it looks like a shot or a grab landed, but it does nothing. If you then compensate by scaling up or down the hitbox to match the art you can make a character easier or harder to hit and that can cause balance changes. Not a thing to be taken lightly.
These are some of the reasons the whole issue of correct scale can be a bit more complicated than just a number change.