You can guestimate to try and mitigate the leaver problem if you form your own group, but the problem is never zero. And ignoring the fact that if I played tank (or heal) I’d have more cherry-picking power in group formation is misleading. But no, no one has magic “knower” group formation powers that skip over this when making a pug … and if you are trying to form as dps or are having to beg groups as dps, yeah, this problem is more present. sky blue, sun hot, etc.
Hell we pugged in one, ONE person and they left halfway through a timed run. it was a mage, right when I saw it was a mage my thought was “could be good, could be spoiled-diaper-baby playing entitled class”. Turns out it was the latter. We just finished with 4 and put him on ignore.