How do the placement games work?

Games Halo 5: Guardians
1

I’m just curious as to how the first 10 games in a playlist rank you? It can’t be just based off wins as a friend and I played our 10 placement games together in swat and I was ranked Onyx and he was only placed into Platinum 1

2

I believe it’s wins and also K/D as the same thing happened to me.

Played 10 games with a friend I did great every game while he did sub par, I got Onyx and he Got Diamond.