I played a lot of different 4X games lately (eXplore, eXpand, eXploit, eXterminate, like the Civilization series, for example), and noticed that most of them suffer from the same problem: As soon as one player got significantly more powerful than the others, that player gets almost unbeatable. The dominant player has access to vastly more resources than the others. Also, that player has a significant advantage in research, which means that the other factions will soon fall back in technology, giving the powerful player even more tools which the weaker factions can not counter, so it makes the game even easier for them.
During this phase it is pretty clear that this player will inevitably win. However, the game usually does not stop here. It continues for hours while the dominant player steamrolls all the weaker players one after another. This poses no challenge to them, because they are so vastly more powerful. So this phase of the game becomes a dull and boring chore for everyone. The dominant player moves their units from one enemy base/city/planet to another knowing that nothing they could encounter there could stop them as long as they avoid some easily avoidable mistakes, while the other players watch helplessly in frustration without any way to prevent their demise.
How could a 4X game be designed to avoid this boring and tedious endgame?