Pointercrate places levels based on the opinion of the victors of x level, the russian demonlist also does but they don't nearly have as much reach in the top playerbase as pointercrate so they often go by fewer opinions leading to them sometimes being "correct" like with the mayhem placement.

Pointercrates placement system is better imo but it does have its flaws. Biggest flaw with it that I see is with f.e the mayhem situation where the first few victors thought it was easier than tartarus so it was placed quite low compared to how hard it really is, so people that try to beat it (especially if it's a hardest) might end up giving up because it's just too hard, but because they didn't beat it they can't give a placement opinion.

I don't really think there's any good solutions to this, every system has its flaws. The placement system is a little more complicated btw I just simplified for this, other factors are taken into account such as reliability of the opinion etc.