Confirmation bias or trend: players who join In-Progress are better, on average

[The_NPC]

unless I'm with my friend as my heal/tank (I'm usually vise-versa) I alway have that in-prog button on... only bias I have seen on my end is I almost never get an in-prog as my Tank class, like 5% are in-prog but 95% are normal, which has made me a bit schechy on SE's qurry system for DF (its even more rare I leave a group as DPS & return to the same group as a Tank... like 1/1000 odds, DF just gives me a norm start group instead)

Now on the topic of "the in-prog replacement is always better" all thou the concept is subjective based on view point I do see some merit to the idea as any time I get a replacement thats the same class as that which left they always out preform (even if near identical ilv)

[Nixxe]

It's possible that since joining in-progress is not enabled by default that people are more likely to enable it when they're more experienced with the game.

It's also possible that if someone leaves a group for a reason other than getting kicked for DCing or AFKing for too long, it's likely due to performance issues and therefore "better" is a very low bar to meet.

In either case, I can't say I've really noticed that, but I also rarely need to fill spots in active runs.