It does mean it's unbalanced. The issue is not whether it's better or worse than an Astral (that's a meaningless comparison, the Astral is for a totally different fleet composition). It's that it has a flight deck, the best missile/fighter-sweeping system in the game, and enough speed to indefinitely kite most ships smaller than cruisers, for the same logistics cost as the two vanilla non-combat carriers, with no drawbacks. That's bad. Due to AI targeting priority drone systems are also much better than they seem to be at first glance.
If you buy two of the freighters, you get the capacity of an Atlas for 2 logistics less at 5 burn instead of 2. They also at least have some chance of escaping in a pursuit. The Atlas is the most efficient freighter in vanilla because it has almost no other advantages and is an incredible liability in combat. For reference the Tarsus and Buffalo are the next most efficient at ~140 capacity per logistics; the Tarsus's advantage is burn drive, and the Buffalo's advantage is being cheap, which isn't really a concern. Past early game you're not deploying freighters as support, so these freighters are best in class with no drawbacks, which is bad.
Funnily the Neerin is actually much less of an issue; I haven't looked at a more detailed stat breakdown, but you get 2500 cargo for 8 logistics (a little worse than an Atlas) in exchange for competent defenses, 1 more burn, and 160 ordinance. Still an overall much better deal, but at least it's not an unquestionably better choice.
The Ox has literally no advantages aside from having a tow cable, and uses 5 fuel/ly. No ship in vanilla uses less than 1 fuel/ly, tug or not. The Luun's only drawback is 4 logistics; if you take out 1 for the tug, you have a 200 cargo freighter for 3 logistics, which is bad but not awful, given that it has shields and mounts. But 0.6 fuel/ly makes all of that completely irrelevant.