Some experienced players might be just a tad elitist or simply "so done" for "herding n00bs", which why it would probably in the long run be better to have some sort of MMR, separate from the level (which you can just grind up even if you suck) that will adjust based on your average performance during matches and generally don't group low-mmr with high unless there is no other option.
teams/groups formed outside of the matchmaking need to have some sort of weighted average for their total MMR rank, for example: higher ranks given a bit more weight so that one low-rank does not bring the whole group down too much so that higher ranking players don't just dominate the whole game alone, oir just eliminate the lowest and highest rank from the calculation as outliers (if more than 2 people) and just use plain average (welcome to statistics 101).