Why am I recieving less mmr for beating players that are higher ranks than me?

Me (Dragunov, 2nd Dan) vs Lei (Expert)

I lost the first game 0-3: -900 mmr

I won the second game 3-2: +80 mmr

I get angry and queue up with Noctis (Expert), get matched with a Yoshi (3rd Dan)

I win the first game 3-1: +1200 mmr

I win the second game 3-0: +350 mmr

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Is this game just throwing the mmr boosts/decreases into a fucking randomizer?

I legitimately do not understand how mmr is calculated, it seems like it's completely arbitrary.

Fuck this dumbass ranked ladder I'm going back to playing unranked