Brand appears to have been the support on your team, but he made the same amount of money that you did even though you got a better K/D/A than he did.
Yasuo had the best CS on your team by far. He was almost 4k gold stronger than you and with less kills. You had more kills than he did, you died less, and you had free farm in the jungle with how much pressure you had with your (undoubtedly) early lead. Despite all this, he still managed to get nearly 4k gold more than you. That's almost 2 whole items stronger than you.
Your rank depends VERY little on your K/D/A. I've gotten S's on Ekko in mid with a NEGATIVE K/D/A because I push lanes so much, ward a lot, and do a lot more for my team than just get kills.
Heck, in one of my last Ekko games, I was something like 5/3/5 and I still got an S. Not an impressive K/D/A, and not a TON of assists either. I just did a lot better in other areas of the game.