I always get confused by the rank grind comments. I have the ranks necessary to buy the Cutter and Corvette. But I never went for the grind. I merely played missions here and there and once while a promotion mission turned up. Even more fascinating: I never did the Empire promotion mission to get the rank "King". I just liked the title "Duke" too much to get myself promoted any further. Despite (as far as I know) I never did the promotion mission, my rank changed to "King" during one of the patches last spring/summer. It guess something there just updated the ranks, corresponding to your faction rating.
So yes, I do understand that those who go the "big ship in a day" route then realize that while they have the credits, they don't have the rank. And if grind was the answer to the problem of credits, then of course it's also seen as the answer to the problem of faction rank. Of course I might just have been lucky and my style of playing just matched neatly to how progression was designed to be. Maybe I am just more patient, for sure I never felt the need to artificially progress my faction rank. This is all based on my personal experience, but at least for me faction rank came easily and naturally, with no grind required.
For me the real grind were old-time engineers and, to some degree, the guardian unlocks. The first I mostly ignored due to how terrible it was. Luckily it is much better now. Still not good or enjoyable, but at least not as disgustingly bad as it formerly was. (Most of my ships engineering was done after the rework of engineers. ) The second was the only thing I ever grinded myself through in this game. The experience of collecting guardian materials actually was great the first few times. But the number of items you need to unlock tech broker items is just too high. You have to repeat the very same thing for so many times, it becomes a chore. And unlike other content, it also doesn't really have any noticeable variation to keep it at least somewhat interesting.
What I mean is: when you really want to grind faction rank, you can of course run the same mission a dozen times. But you can also pick up a variety of missions and run those. You can do different things and still reach your goal in the end, you can naturally integrate that into your normal gameplay. Guardian ruins on the other hand are exactly the same, time after time, and there's no alternative of getting the corresponding materials. And the trip there is so long, you also don't just hop there, do it once and leave again. Just traveling there and back is some serious time investment, so you better make sure you get everything you want and need before leaving again. Which really turns them into an unpleasant experience.