This is a game. It is meant to be entertaining. If you had fun in a match, you'll likely play some more, time permitting. Ergo, if people leave, then they didn't have enough fun to continue (or more pressing issues).
In the end... why do you care about the behaviour of PUGs? I'd be slightly annoyed if my friends left my host without a word but PUGs? There are always enough replacements for them.
High N7 means someone likes to grind. High CP may be an indicator that someone played for a while. On PC both mean next to nothing because people are able to cheat. Sucks for the honest players like me but in the end it isn't important. Sometimes you run into a player with 100k+ CP who uses a Fury with a Striker and dies every 20sec and you simply accept that.
The only thing that counts is fun. I've had duos with <200 CP players who were really good, I've had to carry waves because the high CP players bled out after being stupid. *shrugs*
P.S. Claymore GI. Decent kit. Uh huh. Fascinating and exciting.