Even in normal you get people running 10 rounds then leaving. I have got to 50 yet cos people keep leaving.
-
I was doing legend and our 3rd dipped after 20. We got another who stayed for another 10 then dipped then got another and we got to level 48 before the ADU got blown 😭
-
You could always create your own fireteam and ask them to stay for the whole 50 waves. Also, if you are doing normal, you could just wait until you get backfilled. Complaining about random stranger's behavior will not get you the full run chief, especially when you got other options like I just told you.