I think that you have experienced skewed results in the first game Nex playthrough and should not judge this well-developed, constantly-patched, near-essential mod, based on this one (albeit very well scrutinized from your perspective) play-through.
Give Nex a few more tries!...and look at the long history of players, patching, tweaking, etc. that have gone on. Please take a fresh perspective and see that this mod is in no way shape or form "in beta".
1. "I spent the last 2 real-world days grinding about 4-5million"
IMHO, this is a very extreme take on "sprint to late-game funding" sort of move, taking advantage of the game's current state of "free money via a commission even if I do nothing for my faction" mechanic (which I think the Alex is going to address, and is attempted in Ruthless Sector mod): <-- importantly did your fleet composition also include a battleship or two just for you to swap out in order to fight consecutive end-game fleets as well, plus several fleet carriers and powerful screening elements? Otherwise you may have been cash-rich but fleet-poor.
If I were to mis-time my first colony and lose it...whelp I guess I need 500 Marines before they rebuild that orbital station...and I would try go and take it back asap while the colony itself is relatively undefended.
Personally, if I'm playing to rush-to-a-colony, I try to simultaneously reach at least a "single battleship escorted by three fleet carriers and screen" fleet weight/composition *and* have a million in the bank. While at the same time trying to not have too many "vengeful" faction relations if possible.
2. Yes, events are lively in the Nex galaxy: When events occur...use the intel "sort" buttons and go through in your own priority order whenever a bunch of stuff happens. Nice and slow, game paused.
3. With that kind of cash: also you can buy several very large fleets and assign them to defend your home space.
4. Luddic Path gets annoyed by tech mining, AIs, and potentially other things that I'm not aware of...so I do NOT assign AIs or tech mining at the very beginning. I prioritize ground defenses, a patrol base, and a powerful orbital. I also expect a pirate expedition Real Soon Now and have to have a fleet ready...or nah, I'll just let them come by and peek at the power ground defenses and go away.
5. For all the rest of the comments: this is a big mod that changes things fundamentally, to open StarSector into a 4x experience.
Should a player of native Mount and Blade expect to jump right into Prophecy of Pendor and know how to field an army to win against unique spawns filled with elite troops? Um no. In the first few days of Pendor...hoofa was I having a negative experience until I spent some time reading the forums to get a clue. Even so,
https://pop3.fandom.com/wiki/Dread_Legion *those dudes ATE MY FACE in the first engagement*.
Should a player of X3 Terran Conflict, proud that they just finished all of the Hub missions, jump right into Litcube's Universe/Mayhem mods and expect to win? Not even. There's little hope of having a clue about Litcube's without reading
http://litcube.xtimelines.net/wiki/index.php/Main_Page. Then, one can experience the joys of using MLCC to summon and control a fleet as only Litcube's can offer. After weeks of study. And then it's aaah Bach.