I agree completely- and this is subsequently a source of confusion for me. Doomspace sounds like a great concept - very similar, in fact, to my own plans for a darker Spelljammer campaign.
Why then must we crowbar in an old campaign setting? Why not let Athas be Athas, and explore the possibility of something different for Doomspace? We have Darksun - it's there, it's codified in numerous books, and it can exist in any game the GM wishes to run. Why try and force the square peg into such a resolutely round hole?
This is not a direct response to Charlaquin, but rather my perplexed reaction to the concept of hijacking something that is not Darksun and trying to make it Darksun.