I don't know about NYC groups, but to address the general concern about debriefs, it's probably something that should happen more in general / everywhere.
Find a group that you like and end the session 15 minutes before you *need* to end it. Debrief then, as well as agree when the next session is.
Most often, what happens is that someone needs to leave at, say, 10 pm. 9 pm rolls around and everyone thinks there's plenty of time. 9:30 the last combat starts. 9:55 the one who has to leave is like "lets wrap this up." 10:05 it turns into "come on i gotta go." 10:10 he's packing up while the final round is playing out. Of course nobody's sticking around.
If you agree to play from 6 pm to 10 pm, make it a rule that the last die is rolled at 9:45. Spend 10 minutes going over the best thing and worst thing. Leave 5 minutes to help clean up. It just becomes part of the culture of the game.
Don't insist on having a debrief session so that only you can only complain about it.
Instead of taking valuable gaming time with a debrief, it might be easier message each other after the game with IM, PM's, e-mails, text, ect. The same thing happens but it's not eating into game time. A lot of people have limited time to play and want to use as much of it as possible to game but have time to talk in a non-face to face way between their other responsibilities. I've played with games that had a thread on a message board for this kind of thing and I found it worked out great since you don't have to all be online at the same time for it to work.
Posting online is way less personal and, unless your group has an established relationship outside of RPGs, it's not a very effective way of of changing thing.
Reading between the lines, the OP has a complaint. If the complaint is worth valuable game time, then sacrificing game time makes future game time even more valuable. If the complaint isn't worth valuable game time, then it doesn't need to be brought up.
Watery Soup, they want to "spend a significant amount of time after the game". That sounds to me like more than your "15 minutes" suggestion and is a HUGE ask to carve out of gaming time. IMO, they'll have a much easier time if they are flexible on what form the post game talk takes.
As to more or less likely to change things, I don't agree: often people will say more in an online setting than face to face, especially if they have had time to digest and think about the session without someone asking for immediate and instantaneous feedback.
As to 'read between the lines', IMO it sound like they want to help guide the game more than a specific complaint and , IMO, isn't something that would be resolved in a few minutes after the game but needs "a significant amount of time". To be honest, I don't know what complaint they'd assume they'd have before they join a group...
This is all kind of moot until the OP replies though.
often people will say more in an online setting than face to face, especially if they have had time to digest and think about the session without someone asking for immediate and instantaneous feedback.
I agree people will say more in an online setting than they will face to face. However, I don't think that's necessarily a good thing.
I think you're conflating "message sent" with "message received." If you could guarantee that everything you wrote would be read, and interpreted exactly as you had intended, I agree written is better. But more often than not, either people don't read carefully, or they misinterpret what you mean. Especially with comments intended to be constructive criticism, face to face maximizes the chances that the intended message gets across.
I suggested the 15 minute thing specifically because it limits the comments to only the most important ones. I certainly agree that at no point do I want to spend more than 5-10% of the time allocated to debriefing the other 90-95%.
If you could guarantee that everything you wrote would be read, and interpreted exactly as you had intended
You can't guarantee that in any interaction, face to face or otherwise. What you might lose in context from direct contact you gain in time, both to think about your posts and replies. IMO, a cool down period to digest the session is invaluable for what's bothering you: things can bother you more or less after you think on it a bit. If face to face is a requirement, that too can be done online though it's more complicated: video/voice chat is available to anyone with a computer, tablet, mobile device, console, or smartwatch... Or use a combination of the two, video/voice for basic ideas and posts for the nuts and bolts info.
I certainly agree that at no point do I want to spend more than 5-10% of the time allocated to debriefing the other 90-95%.
*nods* When I still played with a face to face group, we'd generally eat lunch and talk about what we'd play that day and any issue we had before we set up for the game. It's easier to justify the time if you're doing something else too, like food. ;) That and for us, we'd break for the night when people got tired and by then no one wanted to gab.