The total inadequacy of down filled cushions  

maybe yes - maybe no
Lit Up,
Perhaps the quality of the pieces you have examined are sub standard. You do get what you pay for every time.
I do not seem to be having any problems with my Charles Pfister, sofa and club chairs for Knoll Studio® (feather and Spinneybeck Sabrina leather).
I would also suggest, that nothing (even the very best of the highest quality) last forever. The more I drive my car the quicker I require new tires (I must write to Yokohama and ask them why this continues to happen).

I have a Charles Webb down...
I have a Charles Webb down filled sofa that maybe doesn't hold it's shape the best, but it's damn comfortable. And when the cushions go flat, it takes about a minute to fluff them back up to new again.

Nothing beats the comfort of down filled cushions.
I love to stretch out on my sofa in the evening, the cushions mould themselves perfectly to the contours of your body.
Aesthetically its a winner too. I love the look of a nice leather chair or sofa with nicely worn down cushions, it adds character. You just need to plump them up every now and then.

Hi
I don't have any down filled furniture cushions, but I love down in general. That is all.

well..
get down!
Fo' Shriz,
Aunt Mark

Actually,
I like down filled cushions. A local "zen" hotel (Ompany) actually employ's a full time cushion fluffier to keep the down filled cushions looking inviting in the lobby ... like something you'd see on HGTV??...if I had a TV. But I do have a b&b italia den sectional that employs a mixture of foam for the seat, and down for the back. The comfort zone is lovely.
Eat more yard bird, save feathers.
Aunt Mark

Odd complaint, Lit Up?
I take it you've never sat on 50 year old petrified or disintegrated foam.
EDIT: Also why in the blue hell are my "dot dot dots" suddenly turned to question marks on the forum?

oh my god....
lunchbox, I need to stop dotting. It's tired and questionable.
Hello to you,
Aunt Mark

...
...

Damn you all?
?

????? ....... ?????
Period marks turned
into wormy question marks
evil makes me kick.

One of the pieces I'm...
One of the pieces I'm referring to is the Vatne Mobler lounge chair - the cushions are flat as fuck. So what do I do? Refill it with down again? I'm just concerned that the cushions will keep losing their shape. It feels like the cushions are practically empty.

.
No, fill it with cheese, for Gods sake.

🙂
Is that the super Vatne chair you were going on and on about?
When foam dries out, it gets brittle, hardens and crumbles into a fine dust, wich seems quite toxic to me (judging by smell alone).
I would prefer down filled.