The trouble is the other 23 adds you bring into the boss fight with you.
There's only so far you can go with that many randomly matched players before it becomes impractical due to the probability of any such matched group having a few potatoes in it. Exhibit A: The uselessness of LFR in WoW in basically every tier that can't be made virtually sub-CT levels of braindead. Case rested. LOL
The former is great (it seems something lacking in general - to the level of being a zeitgeist issue, there was actually a news comment thread on Y Combinator the other day where parents were comparing how kids sports were in their day to their kids' day: "semi-casual" leagues with a modicum of seriousness have been disappearing there too, leaving the participation-trophy leagues and the super serious competitive travel leagues as all there is. I even have to wonder if younger generations' opinions on team events in general are differently enough colored by that shift as to make it a major reason for people being on different pages here as well?).
The latter would be terrible, because eventually (and for very rapid paces of "eventually" in this community) the leg-up difficulty would be deserted, leaving later comers stranded. Imagine if we had this with EW launch? What's that, you didn't have a work from home job and the place you do work doesn't have a permissive enough policy that you can sit at your desk and do remote desktop shenanigans to game the queue, so you could barely play till the rush died down? The community's words would be all too clear - "TOO BAD." GCBTW, though, right?
It's more than a few weeks, unless it's shifting to another same-role job.
Which is another lovely problem we have here. There's a role shortage, but we don't want those durned DPS to slack on gear, so we don't lower ilvl requirements, so anyone who switches roles midstream like we were encouraging them to? Oh sorry, now you're stuck in crafted and can't join any of the PFs that we need that role for. Lol. Even WoW is better with this (if you switch to tank or healer there, pretty much all you need is a pulse and not completely paper gear and you're in).