Support mains have it bad

I played a really good thresh game and got first blood only one death in the 20 min game because they ff at 20. got my team 32 assists and only got a B+ on the champion master. how are support mains supposed to get level 7 champion mastery when our job is to get the team assists and 32 is not enough? maybe not allowing team to ff at 20 might fix this because i can get more assists before the game is done. either that or have support mains be able to get a S without getting over 32 assists?

Rito from a thresh main fix your shit