Removal of runes is a step to easyer balanceing.
Long post inc, the premise I have is an excessive number of players did not use runes well or wisely. Removal of runes gets removes more of the variable ranges a champions base stats could be. I'm shure many of you reading this right now who have played pre season game have already noticed a in game difference by not having your Armor and MR runes on a squishy champion. This view is from checking hommies pages when trying to help them improve as runes made impact and its being reinforced over and over again as I read the "runes reforged suuucks" threads. Look folks one size runes did not fit all and garbage pages hurt you bad.
Lets be frank here, runes got removed. The mastery system got is usual preseason rework and has been compressed to provide less options with more power. A lot of the power budget from runes has been mixed into this system and I don't think that's bad, but the tree options tend to be fairly focused so its harder to splash defensive traits into an aggressive build, vice versa.
"Ok random internet guy... what does this have to do with balance?" Well hypothetical internet person thank you for asking! Having a lower range on champions starting stats makes every change riot makes to that champion apply better to all players using that champ. Runes where stat balls but you couldn't count on players to be grabbing the right stats. Enemy team is all AD why the hell are you using MR blues? Taking away the 30 places players could missuse stats (plus the reduced mastery points) will make things more consistent on future buffs and nerfs.