Rank system and loot system

So, how does this work? I go 15-0-8 with Xerath and dont get an S+ for the game.

Also, when we get a permanent skin, why dont we have the choice to turn in into blue essence? I've been waiting for anything to use to unlock mastery 6 for him since the new system was incorporated and still haven't gotten either a xerath permanent, blue essence, or the token to do it.