When Microsoft were building TrueSkill2 they looked at millions of data points from Halo 5.
They found that most metrics weren’t helpful in fast tracking rank. Even if there was a positive correlation it wasn’t strong enough (over the win) to justify the data footprint to include them.
There was a discussion point - I think it may have been at GDC, that some of the metrics were actually negative predictors of rank. But still not enough to include them in the system.
The conjecture was that it was assists. And some of this was reinforced with the vague contempt that Josh Menke had for the stat.
So no. Assists are not included. They do not affect your MMR or CSR.
But they are still an important personal metric to reflect on. Are your assists strategic team play - or showing that you aren’t quite good enough to win the 1v1.