I found X4 very different from X3. But I played it at release and refunded it through steam. I really fancy giving it another shot now it’s a bit more fleshed out. I could never get on with the flying in Elite due to its much more hands on nature. X3 is very much a set destination on the autopilot and let her do her thing. The combat is brutal. Very punishing at the beginning and only slightly easier at the end.
What X3 and I would assume X4 is incredible at is empire building. You can build space stations, complexes, shipyards, fleets and trade hubs that will literally break the economy. Its much slower and more focused on the universe you play in rather that Elites focus on your (in my limited experience) immediate surroundings.
The Xenon are a total pain in the ass though but very satisfying to crunch in a all our fleet battle.
Put simply and without hyperbole. If I could save 2 games from the fire and only play them forever 1 would be DCS and the other would be without a doubt X3.