In all other Star Trek series the chief engineer is a Lieutenant or higher
- Lieutenant Commander Montgomery Scott
- Lieutenant Commander Geordi La Forge
- Lieutenant junior grade B'Elanna Torres
- Commander Charles Tucker
And yet in DS9, a huge installation, the most senior engineer is a Senior Chief Petty Officer, seemingly outranked by everyone, even Nog once he stops being a cadet and receives the rank of ensign:
- Senior Chief Petty Officer Miles O'Brien
Why is this? I know that O'Brien's rank is a little unclear through 'The Next Generation' but by the time he arrives at Deep Space 9 that seems to be fully cleared up and the chain of command is clear; O'Brien is outranked by anyone with a name.
Is this because Deep Space 9 is a space station? But in that case why aren't all the ranks lower?