Champion Mastery Level 6 and 7 Requirements

So, I got two S ranks on Thresh and I do not meet the requirements. 500 blue essence seems a bit much while at the same time, opening numerous chests for the right champion shard. You should switch it up by implementing a certain amount of IP to get level 6 or 7, instead of us buying chests and crossing our fingers to get the right champion out of the approximate 131.