@YagyuChan Since one person oneshots most of the enemies, what purpose do any of the other people even have? Even if they follow along they won't get to participate anyway. Are you certain that they do it because they're lazy? Maybe they just learned their lesson and decided not to bother. That is all on the developers. Some people would AFK and "leech" regardless, but you can't be sure about why when we consider the terrible designing of these types of missions. Too many players as all the ones i did with less than the maximum amount were more like it should be. Maximum of 8 people is not too bad. Too bad people mostly wait for full group for no apparent reason.
Besides, wasn't there supposed to be some emergency mission version of this for only 4 people at some point? After that you can call them out with a good reson.