MMR System doesn't work

I had a friend over to play overwatch, he is 4200 sr and we did an experiment to find out more about the mmr system eith my 2200 rated account. He played for 8 hours and i recorded all of his sr gains and losses throughout the day. At the beginning the game very quickly picked up on the fact that he was getting 50 bombs every game and gave him 30 for a win and taking away 15 for a loss. Then he got to 2400 and the mmr system just kind of broke? It started givibg 22 for a win and taking away 23 for a loss. My friend was still getting 50 elims and 25k damage every game and had a 65 percent win rate throughout the day but the mmr stayed negative througout early plat until we ended the experiement. The game allowed for my friend to wreck games time and time again and made no effort to boost him up the ranks? Any ideas of something that we can change to make this experiment more reliable? Or can blizzard tell me how this could have happened,