For the correctness of the MMR aspect: We recognize that there is a tradeoff here on the mmr data quality if the match has solo mmr numbers with party mmr numbers, however we feel that the impact of that data noise is much smaller than even we initially considered it to be early on and generally with how it is discussed online. Most of the issues related to this we think we can solve with better algorithms. Another common case is playing with a friend who has a higher mmr than you, expecting that it will cause your mmr to go higher. While that has been at least partly true in previous matchmaking system iterations, our most recent version does a fairly good job of addressing this. We have enough data to form matches that cause you to have an even chance to win by carefully choosing the opponents that have a similar makeup. At a base level, we think mathematically we are able to have high confidence that playing with a friend will not have a material effect on your average mmr value with a properly balanced matchmaker. We’ve done some testing to make sure this is true in advance of this update, however we know it’s likely there is more work to be done here and we’ll continue working on this aspect in the background during this experimental period.
What actually happens (firsthand but anecdotal experience from years ago; the system probably changes a lot so it may not even be like this any more):
If you win a lot and play really good you get placed into a pool of other people who win a lot and play really good. Then you probably lose but it's not because you're a victim of "forced 50" it's because you weren't actually that good to play with those players, you just won a lot