And if you don't have at least a little context, you don't know what content you need. Or want. Or whatever.
I'm not sure we're talking about tge same thing. It seems like you're still requiring a pre-witten plotline. I'm saying that, if you do, then expecting naive insertion of material, regardless of source, will of course be odd. If, instead, you ask for the material and then start building plot, it's not odd.
If, instead, you mean that material should be somewhat constrained by genre and established fiction but not pre-written plot, then sure, we agree
Insisting that asking the players for content will always ease the DM's workload seems like a fallacy to me, kinda like insisting that running published adventures will.
Of course that's a fallacy, 100% agree. I also don't think anyone's saying that. I might be wrong, there's at least one person in the thread whose posts I can't see. No one I do see has said that.
If I need, say, a cabal of diabolists, it's easier and quicker for me to think for fifteen minutes and come up with 6, plus the leader (and where he's from and why he's doing this) than it is to get in touch with the players, wait for answers, edit the answers, throw out the edited answers (mostly) and use my own ideas anyway. Especially if finding out that there's a cabal is going to be the point (or part of the point) of the adventure.
Yes, if you've decided on a plot then you've already made decisions about the game that means you've accepted doing more work. That's been said a number of times. You don't have to choose this, though. You could ask your player for some NPCs and then riff off what you get to build plot featuring thise NPCs. Or, something else.
Tools are useful if you use them in ways they're meant to work. If you try to use them in other ways, the results can be frustrating. Some tools have been suggested along with how to use them. Most of this conversation seems to be complaining that the tools don't work other ways. Like complaining a screwdriver is a poor tool for driving nails. I agree, it is. I'm talking about using screws, though.