Why do we have to beat diamond players to climb in gold fucking 4

Title, My friend and i are doing rankeds. However i recently got to skip gold 3 so i'm gold 2 now.

Ever since i got gold 2 all of our games are full of plat2 + players with atleast 3 s9 diamond players on their team.

My friend is still gold 4. If he wants to get lp in fucking gold 4 we have to beat players that were diamond one week ago. this isn't just once it's every single game.

How is this a working ranked system? i got to gold 2 by beating gold and plat players. But since i'm gold 2 now the game gives us S9 diamonds every game there are atleast 3 or 4 with the rest being higher plats.

So why do we have to beat diamond and high plat players, for what essentially is not even that much lp in gold 4