Ooh, this is really interesting. I haven't read A5e yet, but I'd love something I can use to run Dark Sun.
Oddly enough, I reached the same conclusion about PF2 vs. 5e for Dark Sun. The keywords system in PF2 in particular makes adapting things much easier. Does A5e have anything like that?
It doesn't really use keywords to the same extent as PF2e, but it's a better choice than o5e simply because of it's greatly expanded exploration tier. As I mentioned, it uses a trackable metric called Supply that is an amalgam of food & water, an expanded selection of activities a PC can perform while traveling (called Journey Activities). While Journeying a PC might cook a meal to get more out of meager resources, entertain the group to keep spirits high, look for supplies for a healer's kit or even material components for spellcasters. Track enemies or scout ahead to look out for trouble, even steal from passers by lol.
Each PC class has something called Knacks (or a similar mechanic) that are specifically abilities you can learn and use while exploring. For example Rangers have knacks that make them great foragers, give them the ability to produce minor healing potions called salves, construct long-term shelter that lasts potentially forever and protect from weather & even attacks in the night.
On top of this, there are encounter tables for each tier of play separated by terrain. These aren't necessarily random monster encounters either, they could be a traveling merchant who makes camp with the group, a natural garden filled with supplies, or other strange things. For specifically Dark Sun, there are tables for Blasted Lands (devastated landscape), Fiery Hellscape (volcanic mountains, etc), Haunted Lands (abandoned villages, undead-haunted settlements), Lofty Mountains, Open Roads, Parched Sands, or even Tangled Forest for the rare jungles that exist on Athas. There's a page on creating your own Regions.. so I'd probably add like Silt Sea & Salt Flats, Dust Sinks.. etc.
Long post I realize, but there's so much here that supports a great exploration tier. I haven't even gotten into things like travel scenery, creature signs (footprints, rubbed off bark suggesting a nearby bear.. etc), exploration challenges which are pages of non-combat encounters that test the PCs skills and are usually exploration/survival based.. such as inclement weather, collapsing structures, fields of battle, back alleys, fairy rings, forest fires.. pages and pages of them and they are all awesome.
My first a5e campaign isn't going to be Dark Sun... instead I plan on making use of the Zeitgeist setting due in a few months for campaign set on the high seas, involving a naval war the PCs become embroiled in; but without a doubt there hasn't been a d20 TTRPG this suited for Dark Sun since 3rd edition D&D.
FYI the kickstarter is expected to start accepting late backers in the next week. You might want to consider it.
