Thanks everyone. I realize I definitely made some mistakes in the OP but I got a lot of good answers regardless. For the record, I was definitely stuck on HM Titan for upwards of 5+ hours a day for almost two weeks. This is before I met my FC and the large group of talented players I'm lucky enough to play with now.

It seems like:
A lot of players can't find a group for completing content that meshes with their schedule/playstyle, and duty finder/party finder are incredibly frustrating/stressful when you have something you want cleared, because it's difficult to put together a group of PUGs "on the same level."

For players seeking progress, they don't want to be matches with newer players who are learning because there's no incentive to teach them the fight. Especially in duty finder your chances of meeting a player 2-3 hours later once they've learned the fight is incredibly low. It's a waste of your 60 minutes to wipe repeatedly because the other players have less experience than you.

For players seeking to learn, they don't want to hold back the players ready to progress. They don't want to deal with belligerent attitudes about how they "should have watched a video" or "what do you mean you don't know the fight?" This is completely understandable, dealing with mechanics can be stressful enough even without dealing with the players.

Plenty of players are playing at their own pace and simply haven't come to the "endgame contents" but are easing into them, but are wary of running into people who expect you to have already cleared the content.

A few people have really sad stories about their statics, and I feel for them. Most of the higher level content is tuned for a group to complete together, rather than a number of individuals.

It feels like, to me, that a lot of players would be happy with a sort of "CT level difficulty" version of coil, that offered lesser rewards, but roughly the same type of story and battle experience.

I guess a sort of "stress free" group approach introducing the fresher players to new content is definitely the way to go, more or less confirming what I thought. Let's go in for an hour, wipe a bunch, laugh about it, and come back another day/when you feel comfortable. If we knock it out, great! If not, no big deal. At that point you at least have the minimum about of understanding to want to join a party finder/duty finder group.