What kind of Astral Plane would you have prefered to see? I'm not familiar with its depiction in the other editions so I looked at it with fresh eyes and took to it quickly.
The depiction in Manual of the Planes, also 4e, was fine, really. It lacked the Border Islands and 'Outsiders," IIRC, which were the parts - injustice & refugees in the afterlife?- that kinda grated on my sensibilities.
I think the reason Exalted move on is simply because the Dominions are no longer at full power. They can't 'Hold' on to them anymore.
That's reasonable, conceptually. I find it, just off, for a cosmological/afterlife explanation, though. Kinda the same way I never cared for Planescape. At some point, the grit should precipitate out.
The afterlife should be, well, supernal in some sense, at least for the Faithful who lived & died on the side of Good.
...I guess it also taps into the 'tude of things like Gaiman's
Good Omens, which I can't fault it for, either.
Personally I loved the lore related to the
Lattice of Heaven and Erathis' obsession with it. It made it clear the Dawn War had far reaching impact and ,,,The Astral Sea is essentially broken, which makes it an exciting place for adventures instead of some kind of perfect heavenly plane.
That part I can agree with. The Lattice, a fall from grace, a subsequent obsession, even for a deity, all fits, has an epic sweep and a mythic quality. If it were just, or even mainly, Erathis & her worshippers that were paying the price for her hubris. If the Astral Sea & the Lattice were 'broken' but at least /some/ of the Domains were models of a credible/just afterlife.
It's not like it's a terrible idea, and it /is/ consistent with the PoL theme that holds through Heroic & Paragon.
Edit: One of my players like to joke about the sigil sequences used in teleport circles being 'chevrons' like Stargate, the more I think of it, the more the Astral Sea feels like a Stargate-esque setting. I should drop the odd Ma'Tok Staff and Zat'nik'tel.