You really haven't played much D&D have you? A D&D party is almost always made of crazy powerful party. Hell at the higher levels(18-20) D&D parties can end up against some of the craziest stuff imaginable like gods and leviathans and deal with reality bending powers. There are no simple "this guy just wants a friend" characters in a D&D party.
I have played a decent amount of D&D. I haven't played all of the way up to level 18-20 because going up absurdly high in level seems foolish for the very reasons you list and there is a reason there aren't a lot of campaigns made for those high of levels. At least there wasn't when I played. I also didn't make every character I ever created some over the top story, because it isn't required to have fun or tell a story.
Also I believe Imoen is the first companion you ever meet in a Baldur's Gate game, if I recall. And she is literally just some girl that you grew up with who doesn't have many unique or special qualities about her at all... and she is LITERALLY just your friend. She quite literally just wants to follow you around and help you out because she is loyal to you.
Now - she becomes more powerful as time passes because she is adventuring and gaining experience. But she wasn't on a mission from a god. She didn't have a nuclear bomb in her chest. She wasn't a tortured vampire. She didn't make a deal with a devil. Not that any of those ideas are some awful thing - they are fine. But as williams85 said, not everyone has to be a 'chosen one' in a story.
I guess I will wrap up by saying...
1. I think the first game proves you wrong.
2. Your D&D games sound like they would be abysmal, like a fight for everyone trying to be more important and 'cooler'/'more powerful' than the next character. You should try branching out a bit.
