Heroes can't be interesting? Do heroes have to be superhuman?
I dunno, I just think hero is a weird construction for Trek characters. Like, as a kid I watched TOS even before TNG came out (which happened when I was 8). I never, ever looked up to Kirk, Picard, or anyone else. I just thought they got to go on awesome adventures and daydreamed/wished that I'd be able to as well. Maybe I imagined myself on the ships sometimes. But I didn't myself as being one of the characters.
Then again, I suppose, thinking about it more, I don't think I've ever looked up to or been inspired by anyone in my life, fictional or real. I'm grateful when people do incredible things to help other people - and on occasion I wish I had the virtues of others - but generally speaking I don't spend much time comparing myself to others.
I'm not interested in watching a Star Trek series about unremarkable people. I like to imagine if we're seeing their adventures on television, it's for a reason. I'm in general not interested in watching shows about ordinary people in ordinary circumstances. If I were, then I wouldn't be a fan of science-fiction.
Science fiction is about - by definition - extraordinary circumstances, but characters can be quite ordinary people who are thrust into these circumstances.
But there's a difference between a character being interesting and a character being a demigod. Miles O'Brien was a pretty ordinary guy, but he was also an interesting character.
What science fiction franchise have you been watching, exactly? To be honest the only characters in trek who I would deem normal is Jake Sisko, and probably Nog. The rest of them are genetically enhanced, or androids or the only freshman to ever win the Academy decathlon, brilliant tacticians, brilliant scientists, half-vulcan, half-klingon, half borg, or prodigies destined to walk the stars with some weird alien. They are all larger than life in some way, there is nothing normal about any of them. And dare i say that of course these characters are heroic because they take actions and make choices that most of us probably couldn't when it really came to the crunch.
As I've said in the past, I'm more of a science fiction reader than viewer. Years back, I read a series of essays by David Brin about Star Wars versus Star Trek which encapsulate what I'm talking about.
Basically Star Wars is a retelling of romantic, heroic fantasy with some sci-fi trappings. The main characters are "chosen ones" who in some cases have magical powers which set them above normal folk. It is their destiny to be great, whether for good or evil.
In contrast, Star Trek concentrates on a group of intelligent professionals in a workplace setting doing their best with their abilities and internal moral compass to navigate thorny situations. It's explicitly not a "chosen one" universe, but one where free will and rationality rule the day. One of the central rules of the Trekverse (sometimes violated, but usually followed) is just about every being you meet - from a seeming god to a total monster - is just a different kind of person which has all of their own foibles.