For everyone complaining "HOW IS THIS ONLY AN S-/A?!?!?"
The ranking system is based off more than your KDA.
CS is a huge factor that people completely ignore. Objective participation is a factor. Warding is a factor. It also factors how well you did comparatively with the rest of your team. If you went 15/2/20, but only have 130 cs and 4 wards placed in a 40 minute game, you're not getting an S+ and you don't deserve it. You don't deserve to get an S+ for a game where you farmed kills and didn't push objectives. Pretty much every one of these threads the poster has an awesome KDA, but non-existent warding and CS. Get kills then push objectives with the numbers advantage to end the game. Don't get kills then dick around for the next 20 minutes BMing the enemy team.
The system isn't designed to reward people for dragging out complete stomps over pushing objectives to end the game