Very confused about what's going on here from a MMR standpoint and was hoping somebody with better understanding of the system can explain.

I never play Valorant solo - I always duo with a RL friend of mine that floats between Ascendant 1 and 2. His peak is Immortal 1. My rank is generally always D1/D2. My peak is D3. I usually 1st or 2nd place on my team 80% of the time, my friend is usually in the bottom two despite his higher rank (his 5 stack helps keep his rank up), and his presence routinely brings high Ascendants or Imm 1s into my games.

I'm starting to get frustrated simply because I'm routinely performing against equal and higher ranked enemies but don't feel like I'm getting anywhere. Just like everyone else, I routinely run into games where people go AFK / don't communicate / go into major depression 40 seconds into round 1 and try to forfeit, say gg, suicide until the game ends. These games give something like a 22 - 25 RR loss no matter my personal performance. Last night, I do a duo with my friend, who gets on his Plat 3 smurf at my insistence, and then this happened. 10 RR for a win and MVP. My game was literally all plats and golds, with a 10 - 20 Reyna on my side. I was the only Diamond.

I'm not understanding how that happened. Why would I even get matched against ranks that low where I'm assuming my downside would have been 26 RR and yet my MVP upside is 10? Is this how matchmaking is supposed to work or is something fucky going on with my MMR for constantly duoing with someone 3 ranks higher and keeping my rank at a virtual standstill? I'm definitely starting to get a little bitter because I just wanna grab that green and that +10 made me go wtf.