I don't know about the rest of the game becoming irrelevant if we pull off diplomacy, but we'll see.
I meant for me.
For me, a good 4X would be a 4X that makes the diplomacy interesting and viable. As much as I enjoy the ship design (e.g. Space Empires) I've never been fond of the empire day-to-day management (AI War fits right into the right slot in that regard: I've got resources, production, and expenditure, but don't have to get super fiddly with how X the Y is because of Z,* though a few other games have done well too, like Age of Wonders). But you've already nixed the part I've
really hated: dealing with stacks and stacks of unit stacks worth of combat and having to auto-resolve or manual-command two dozen fights a turn.
Early game I'd participate and manually command each fight, because I was smarter than the auto resolve (most of the time: Age of Wonders I would still auto-resolve ranged units because it was impossible to figure out if moving the unit this way or that way would improve their trajectory with no 'shit that was the worse idea, undo undo!' button) but as the game progressed I'd use more and more auto-resolve just to get them done and over with and rely on tech and numbers superiority.
*TLF is just the other side of the line for me. TLF had a lot of civilization attributes with no obvious way to affect most of them with mechanics going on that you have no control over that have a greater impact. I'm sure this has changed since release, but I feel that it was still a lot of abstract numbers, most of them hidden, buried, or poorly explained with only two levers available to the player: neither of which seems to have any impact.