Which is supposed to be the limiting factor in hextech?

I'm confused as to which resource that riot thought was going to be the limiting factor in opening chests. They put in a timer system that you can only get 1 chest unlock per week but I cant get enough keys to open the chests I have. I'm sitting on 4 chests right now and have 1 fragment, of which I've had at least 9 wins since I received that one.

Assuming I win 50% of my games that is 18 games played at around 8-9ish hours without 1 key fragment so assuming I get one on my next game that means without playing 30hours or so a week I will always have more chests then keys. Now I understand the system is random but every fragment I've got has seemed to be pretty close to the same waiting period as this one like 10% chance on wins.

At the very least they should make it so you can purchase the fragments with ip or something. Or up the drop rate to something at least like 30% of wins because even at that it would take about 10 hours of play a week to get a key.