5 Man in Flex Should Ignore Rank Restrictions
CS:GO has a policy in place that I think is really smart. Usually in the ranked matchmaker there are restrictions based on the rank of the players. If the difference in rank is too great, you don't get to play together. This is obviously to avoid screwing over your teammates by having the equivalent of a Bronze player in what could be compared to Diamond or Challenger level games. But when the entire team is all premade (meaning all players have agreed to play with each other), the restriction isn't enforced.
I may be wrong, but the way I believe that the matchmaker deals with the possibility of one player being disproportionately high elo (1 very highly ranked player with 4 low ranks) is that the lower ranked players are largely ignored, so you don't get situations where one player takes over the entire game. Being dragged into a difficult game shouldn't be too much of an issue for the five players that have agreed to this beforehand.
It isn't a super pressing issue, but I think it's a nice possible quality of life change that would let 5 friends of very different skill levels have an outlet to tryhard without making the game worse for their teammates.