I do agree that composition and skill with affect the percentile a player can reach, but I do strongly disagree with the statement that looking at a percentile is completely worthless too.
It's up to the individuals looking at the logs to see where they can improve and where they're doing well. A percentile gives that player two things: (1) a range of where they are in terms of skill level with the rest of the player base in the same content and (2) gives them a metric / goalpost to aim for.
Also, a 80th percentile player playing in a group that is a 20th percentile skill won't suddenly make their DPS bottom out at the 20th percentile. It'll dip, yes, but I don't believe it'll dip further than a +/-10 percentile range. That's still a sizable gap but it doesn't make things worthless. A highly skilled player will be able to make non-optimal conditions work for them and can adapt to optimize for the conditions they've been given.
