The X series. Try X3 reunion, or X3 terran conflict.

tbh, there is a bit of a steep learning curve / bafflingly bad interface thing going on with them but theyre the best of those kind of games imo.

Theres also elite dangerous, but I could'nt rally get into that. Because the galaxy is real sized with billions of stars everything is necessarily samey and bland. Also its sorta like an MMO you need to be checking out forums and engaging with the community to actually find out what to do. I do not want that from my privateer-likes. I want to just be able to completely immmerse myself in the game and explore on my own and find cool things and possibilities and implement my own schemes.

There's a ton of them. The "official" one was Freelancer, though.

To expand on this, I feel like there's a lot of Privateer successors, but few-to-no WC successors.

There's privateer remake https://sourceforge.net/projects/privateer/files/ (supposed to have a homepage here: http://privateer.sourceforge.net/ )

Disclaimer: Ages ago I coded the GPL Vega Strike http://vegastrike.sourceforge.net/ engine on which the privateer remake operates -- you might need to run in xp compat mode unless you checkout the data dir

I think you could say that Star Citizen is the modern spiritual successor to the Wing Commander series (and is being created by the same person, Chris Roberts).

I wonder why SC has had such a prolonged development period. It seems a game that's bound to never fully launch; or have a Duke Nukem 3d-like end product. I bought into it early, but I've never been able to enjoy it once so far.

FYI, in this comment section there's a lengthy discussion regarding Start Citizen's development; lots of good answers to your question there.

Also, there is Avorion, Starpoint Gemini: Warlords, Evochron Legacy, Rebel Galaxy, and Endless Sky!