What is with this ranking system??!!!

Games Other Halo
1

Me and my friends just qualified for Breakout, all 4 of us played all 10 games together.
We won 9/10 games, we even beated teams consisting of onyxes and 1 with a champion.
But what did we get?!
Myself: a diamond 4 with a 1.2 kd.
Daniel: an onyx with a 0.8 kd.
Cameron: a platinum 4 with a 1.9 kd and he won several rounds on his own VS 4 guys (YET PLATINUM???)
Lewis: an onyx with a 1.5 kd.

How just how did these ranks happen?
I thought the ranking system was purely WL based so how come our ranks are so damn different?
How come the best guy in the team go the lowest rank and one of the worst got the highest?

2

I know squat about how the placement matches actually work as I’ve seen people claim some very strange results.
However, things we know (It may be incorrect though)

-Last season ranking plays a role in your new rank
-Placement matches isn’t entirely about W / L but also individual performance
-Ranks of those you play matter
-Highest attainable rank from Placements is Onyx 1700

Anyone may correct these at their pleasure.