It'll be almost impossible to get traction against a service that is already serving the community well, as with Stack Overflow. There are many gripes about Stack Overflow (which is common with success), however it still actually does its job well. To beat them you have to be drastically better (as it is they have to become a lot worse, or it'll require a technology inflection that they miss).

You're entirely correct about the only way to approach it, bowling pin wise. You have to narrow and find something you can own, something you can beat them at in a big way and grow out of that niche. Otherwise something broad like this risks languishing with small amounts of activity across many topics and not enough answers or questions per to really get momentum rolling to sustain it all.