It seems like among DS9's main staff, people like O'Brien and Kira get the worst luck. They're basically normal people who have picked up some skills thanks to a past fighting Cardassians, but they work with some people who have the golden ticket to talent. A genetically-enhanced doctor, a shapeshifting security chief, a captain who's basically the son of the Prophets, a Trill with seven lifetimes of experience...it must be a lot of pressure working with peers like those! And then there's Worf...I mean, he doesn't really come with inherent bonuses that other Klingons don't, but as a Klingon he can kick some major ass... I don't know. Wouldn't it suck to be the normal guy in that place?
I don't know that I would describe Kira, with her prior life, as "normal." O'Brien is the regular joe on the show, he has a fairly normal marriage, a couple of kids, hobbys, isn't a genius, just kind of generally smart. He isn't a officer, he's a grunt.
Normal folks at least have some chance in engineering. The sciences seem to be reserved almost entirely for the super-human aliens, robots or cyborgs.
Engineering is science. I can't imagine you could understand the works of a 24th century space station or starship without being brilliant.