Why?

Why in a gamemode designed specifically to test your skill level against other players of equal skill level [Ranked] are 4v5s counted as a "loss". Thats like having an olympic race where 4 players race against 5. Sure if the team with 4 has an insanely good player [fed ally] they can win. However if they are all equal in skill and have similar kdas when it comes down to it that is unfair. So why is your rank based on unfair games?