Not all the time. I have a lot of pictures that the boss just drop purples all the time. I preferred chests instead. Sorry. And it’s also a big chance to get a MW from Elites. That’s why is so boorimg just killing a boss.
Because for "reasons"( I hate that excuse Ben Irving), Bioware decided to 'streamline' the match making process and not put in a que controlled by the player. Normal/good match making has a notice that says, "There is a match in progress, would you like to join?" If you decline it puts you in a que. Oh wait. An indy game called Vermintide and Vermintide 2 does that. But for 'reasons' a AAA game publisher and developer can not.
TLDR: Starting a mission can act like quickplay for 'reasons'.
The "reasons" are fairly easy to guess. If 4 players don't queue for the same mission at the same difficulty within X seconds of each other normal match making is abandoned in favor of quickplay match making. There is no option to continue waiting because as a AAA game it was developed with the expectation that the player base would remain large enough that getting pushed into quickplay would rarely happen. It likely never even crossed their minds that this might be an issue this soon after release.