Answers can be from Canon or Legends.
TL;DR: How do the senior Imperial Navy Officers with experience in the Clone Wars account for why a powerful force-using 'baddie' like Vader not only does not overthrow, but faithfully serves an apparently non-force-using human politician in the form of Emperor Palpatine?
I was re-watching ROTJ, specifically the scene where Vader arrives at the second Death Star and is speaking with Imperial Moff Tiaan Jerjerrod, when the following exchange took place:
JERJERROD: Lord Vader, this is an unexpected pleasure. We're honored by your presence.
VADER: You may dispense with the pleasantries, Commander. I'm here to put you back on schedule.
JERJERROD: I assure you, Lord Vader, my men are working as fast as they can.
VADER: Perhaps I can find new ways to motivate them.
JERJERROD: I tell you, this station will be operational as planned.
VADER: The Emperor does not share your optimistic appraisal of the situation.
JERJERROD: But he asks the impossible. I need more men.
VADER: Then perhaps you can tell him when he arrives.
JERJERROD: (Terrified) The Emperor's coming here?
VADER: That is correct, Commander. And he is most displeased with your apparent lack of progress.
JERJERROD: We shall double our efforts.
VADER: I hope so, Commander, for your sake. The Emperor is not as forgiving as I am.
JERJERROD: (Big gulp)
When Jerjerrod finds out that the Emperor is coming for an inspection he seems very afraid by that fact, more afraid (and as is implied by Vader's comment that the Emperor is less forgiving than Vader is) than he is of Vader himself.
This led me to wonder why this would actually be since, according to this question and this question, very few people know that Emperor Palpatine is a force-user, much less a Sith (NB 1). While thinking about this, I also considered several points about the Palpatine/Vader relationship:
a) While many in the galaxy at large didn't really know about the Jedi, the Imperial Navy was full of officers who served in the Clone Wars and thus would have either seen, met, or at least heard about the Jedi and their use of the force.
b) Vader never hid his use of the force from his officers or his victims, and yet Palpatine was very careful to limit his use of the force in front of others, or to kill those who saw him doing it.
c) According to the official storyline that the Empire released, the Jedi tried to overthrow the Republic and attacked Palpatine in the process, but the GAR saved Palpatine and he ordered them to wipe out the Jedi.
d) The Imperial Officers who served in the Clone Wars (NB 2), whether they believed that story or not, especially the more senior ones who would have read field reports or worked in intelligence and so on, would not only have known about the Jedi and their use of the force, but would have known the difference between a 'good' force user like Obi-wan or Yoda, and a 'bad' force user like Count Dooku or Asajj Ventress.
e) The 'bad' force users these Imperial Officers would have encountered during the Clone Wars engaged in horrific war crimes, did everything they could to gain/increase/hold power, and used any level of violence required to get what they wanted, whereas the 'good' force users eschewed violence as much as possible, didn't harm others unless necessary, and didn't seek out power. Of course these are generalizations, but I believe they are borne out by TCW tv series.
f) Thus, these senior military officers are unlikely to have mistaken Vader for being a 'good' force user, whether or not they knew about the Sith, or what they thought Vader's backstory actually was.
When you put the previous six points together, the picture it seems to paint is that the higher echelons of the Imperial Navy either knew, thought, or were told that the Jedi were the bad guys, that the Jedi had been (mostly) destroyed, that the Emperor was just a normal non-force-using human politician, and that he was served by an incredibly powerful force-using non-Jedi. And yet at least some of them seemed to fear the Emperor more than Vader.
I can understand the argument that if someone as powerful as Vader served the Emperor, the Emperor must be even more powerful, but if these Imperial Officers had direct experience of 'bad' force users doing everything they could to get as much power as possible, what is the in-universe explanation to the senior military officers as to why Vader not only doesn't overthrow the Emperor and rule in his stead, but serves the Emperor so absolutely, considering the fact that they know Vader is a force-user (and one who uses the force in a way very similar to how the 'bad' force-users used to), and do not know/believe that Palpatine is?
NB 2: Please note that I am not asking about Tarkin or Thrawn here, but the senior Imperial Navy Officers in general, particularly those that served in the Clone Wars.