clearstream
(He, Him)
I agree that context influences ideal rest duration. Some might like to have mutable long rest lengths. I favour fixed and seem to have found a value that - at least for my narratives - works very well.It's not an either/or. Duration can only matter when circumstances are taken into account, precisely because those circumstances can change.
Playing a Dungeon bash? It may be enought to say the dungeon is simply not safe enough to take a long rest - seems reasonable. Lots of Wilderness? It might be enough to say that a wilderness environment where you have to set watches is not safe enough. Or you could push it out to 36 hours and that may be enough - you probably don't want to linger for that long in any environemt that is remotely dangerous.
What about urban adventures? An 8 hour long rest becomes unworkable.
When it comes to strategic power, my experience has been that a longer and less interruptable long rest creates interesting problems for players. I guess that entails an argument that strategic power is not an ends in itself, but only worth having if there are interesting problems to overcome. It's easy to give players power. Making them feel like they have authentically overcome challenges is another thing.Yes. But I think it's important to realise that the biggest benefit of this is flexibility. It puts the strategic power in the players hands. That's why changing long rests is so particular to the style of game you're running. I tend to think it works better (at least in terms of keeping the strategic power in the players hands) to keep the long rest as short as you can while enabling the particular type of game you want to run (which may still be much longer than the default 8 hours.)
I also think it's worth considering how to keep a certain kind of power in the players hands and maintain flexibility.
Like for example keep the long rest at 8 hours but only once a week.
To my taste, the longer rest also produces a more reasonable magical-economy... but let's face it, fantasy world economies are unlikely to be much more than on-surface plausible! So I would make no great claims about it. The obvious example is on revival magic, which for me becomes far more interesting when it is less available. (It wouldn't surprise me though, to find a DM running a very interesting world where dying was in fact very hard to achieve.)
As an aside, there is a tension between empowering players and challenging them. The choices made produce pay offs in different places.