Is getting a S rng?

I just had a game as yasuo that I went 25/8/11 with 238 farm. Our lee sin was 16/7/13 with 203 farm but got a S at the end of the game... I did not. We won the game too. I would honestly say that I played the best I ever had on yasuo (been practicing him so much) and thought for sure I had secured a S for the first piece in my mastery 6 token. I had a A +???? How is that possible when I had more farm more kills than our lee? I felt robbed because I had carried this 52 something minute game. What else can I possibly do? Die one less time? Get ten more kills? Riot please I honestly had a amazing game but can not get a S. is there any way you guys can make guidelines for how to get s-, s, and s+? I know that it might make people greedy for kills or farm and make teams more toxic so I was thinking maybe make it more vague like: get more farm than opposing laner, die less than everyone on team or however else it's possible to secure an S. would love feedback from riot and the community I've had this problem with other champs too. What can I do?