Matchmaking issues

This is a real discussion to try to understand what happened I lost this match and I'm fine with it But i just cant understand why this match could happen

https://cdn.discordapp.com/attachments/293500383769133056/377970102634676225/image.png

So i'll use some maths to add clarity what i mean :

League : each rank gives +5, starting at +0 from Bronze Division : 6 minus "current rank "

Bronze 5 => ( (5x0) + (6-5) ) = 1 [...] Bronze 1 => ( (5x0) + (6-1) ) = 5 Silver 5 => ( (5x1) + (6-5) ) = 6 Silver 4 => ( (5x1) + (6-4) ) = 7 [...] Silver 1 => ( (5x1) + (6-1) ) = 10 Gold 5 => ( (5x2) + (6-5) ) = 11 Gold 4 => ( (5x2) + (6-4) ) = 12

ENEMY TEAM + 10 (Teemo) + 7 (Yasuo) + 12 (Udyr) + 2 (Brand) + 7 (Zed) = 38

.

ALLY TEAM + 6 (Ryze) + 6 (Grave) + 7 (Jinx) + 7 (Kennen) + unknown (Zilean) = 26 + unknown

Calculating the value matchmaking estimated for me, if the match is considered fair : 38 = 26 + unknown unknown = 38 - 26 unknown = 12 => Gold 5 ?!

TL;DR I lost a match, they played well I'm very confused but not salty I did some maths I am NOT a Gold 5 player ! Even if i was, i don't want to be forced to carry an entire team I find the matchmaking questionable

Anyone getting else getting questionable matchmaking ?

Bronze and Silver are the biggest and most populated leagues I don't understand why matchmaking have issues to find enemies that have my level But instead gives me enemies above my level