I mean on Enterprise D he was a transporter guy, then all of a sudden he's this miraculous engineer who can make a replicator out of scrap iron.
Did it make that much sense that the Federation would have an NCO as the chief engineer of an important space station?
Also, wouldn't he have to command engineering officers who technically outranked him?
I don't understand how it works in trek, but most times the engineering staff will at least have a lieutenant.
I do remember something about him turning down being promoted to an officer, but how does that work? If he even has an ensign on his staff, they outrank him, you might say he's the chief engineer so hee's in command, but when an Admiral rocks up on a starship or Ds9, the captain has to do what they say. I'm pretty sure Starfleet would have basically said you have to take the promotion to do this job, if you don't take the promotion we are moving you to a less important job, back on the transporters for you, O'Brien.
it just didn't seem well thought out to me