According to novels Lords of the Sith and Tarkin, Palpatine purposely put psychopaths (like himself) in charge of Empire, i.e. in top ranks. Upper-middle and middle ranks (where Ozzel belonged) were filled with incompetent but politically loyal buffoons, slothful degenerates and backstabbing careerists. Those at the very top and under personal thumb of the Emperor were unable to reconcile their differences and join forces to topple him, but did share his vision of ruling through fear and terror. Those in middle positions knew too well that they owed their position to the Empire and the Emperor, not to their own skills. So they remained loyal to keep their rank and their life. Lucas was probably influenced by Stalin's Soviet Union, especially before WW2 .
Vader was probably personally disgusted with such policies, which often brought defeat, although Empire had vast numerical and technological advantage over the Rebels. That is why he often vented his frustrations on Imperial commanders whom he deemed incompetent. In this case, Ozzel paid for promotion above his abilities with his life.
Fruun was one of Belkor's men, one of the hundreds whose loyalty he'd bought through favors or secured through blackmail. Moff Mors-lazy, sloppy Delion Mors-left the running of Ryloth's occupation to Belkor, and Belkor had not been idle. He'd filled several Imperial units with commanders whose first loyalty was not to Mors, or even to the Empire, but to him, and the soldiers would do exactly as their commanders told them.
After Murra had died, she'd found herself purposeless and content in her purposelessness, just drifting. She'd turned hedonistic, grown lazy. Worse, she'd lost her ability or desire to discern a quality commander from a flatterer. So she'd promoted Belkor and those like him, while ignoring people like Steen Borkas. And now she'd lost a Star Destroyer, the Emperor, Lord Vader, and maybe a planet.
The Emperor chuckled. "Delian Mors is many things, Lord Vader, lazy, hedonistic, nihilistic, but she is not and never will be a traitor to the Empire. And after today's events, I suspect that she will begin correcting her weaknesses. Proceed, Sergeant."
"He is fearful of you, as he should be, but he is not as timid as he seems. He will do as he's asked in order to preserve what power and privileges he still retains, but he will do no more than what he's asked. And he will do it all with an eye first to his own interests, then to his people, and then to the Empire."
"Hmm. Would you say then that he is...loyal?"
"Viewed through those constraints, yes, I'd consider him loyal."
Lords of the Sith
The Emperor studied him openly. "I sometimes wonder, though, if you-born an outsider, as I was-feel that we should be doing more to lift up those worlds we defeated in the war? Especially those in the Outer Rim." "Turn the galaxy inside out?" Tarkin said more strongly than he intended. "Quite the opposite, my lord. The populations of those worlds wreaked havoc. They must earn the right to rejoin the galactic community." "And the ones that waver or refuse?" "They should be made to suffer." "Sanctions?" the Emperor said, seemingly intrigued by Tarkin's response. "Embargoes? Ostracism?" "If they are intractable, then yes. The Empire cannot be destabilized.""Obliteration." "Whatever you deem necessary, my lord. Force is the only real and unanswerable power. Oftentimes, beings who haven't been duly punished cannot be reasoned with or edified."
The more Sidious investigated Tarkin's past-his unusual upbringing and exotic rites of passage-the more he grew to feel that Tarkin's thinking about the Republic and about leadership itself was in keeping with his own, and Tarkin hadn't disappointed him. When Sidious had asked for help in weakening Supreme Chancellor Valorum so that Sidious himself could win election to the position, Tarkin had stonewalled Valorum's attempts to investigate the disastrous events of an Eriadu trade summit, thereby helping to foment and hasten the Naboo Crisis. Tarkin had remained loyal during the Clone Wars as well, enlisting in the military on the side of the Republic, despite repeated entreaties by Count Dooku-which Sidious had arranged as a test of Tarkin's dedication.
Still, Tarkin could see how a Republic officer like Teller might feel betrayed to the point where he would attempt to wage a campaign of revenge against all odds. The military was filled with those who refused to accept that collateral damage was acceptable when it served to further the Imperial cause. In the absence of order, there was only chaos. Did Teller expect an apology from the Emperor? Compensation for the families of those who had been unjustly executed? It was witless thinking. Multiply Teller by one billion or ten billion beings, however, and the Empire could face a serious problem˙...
As the backbiting between Rancit and Ison continued, Tarkin was tempted to raise his eyes to the podium to see if the Emperor was smiling, since it was his policy to encourage misunderstanding as a means of having his subordinates keep watch over one another. A form of institutionalized suspicion, the policy had proven an efficient fear tactic. He recalled Nils Tenant's wariness in the Palace corridors. The competition for status and privilege and the jockeying for position brought to mind the waning years of the Republic, but with one major difference: Where during the Republic era cachet could be purchased, present-day power was at the whim of the Emperor.