No, it's pretty much a given that everyone will have their happy ending. Gosho doesn't do sad, depressing endings. Even in Conan, any sad and depressing "ending" is later proven to be not the ending. Kogoro and Eri is the only couple where there's any doubt, since it seems like Gosho Aoyama likes to keep them bickering and never getting anywhere with their reconciliation. I can totally see them still bickering at Shinichi and Ran's wedding.
I don't really see why people think fiction should necessarily be realistic. When I read or watch fiction, I do it to immerse myself in a world which gives a sense of hope unlike real life and where rare but good things are more common.
Absolutely. But we have every right to find repetitive nonsense boring as hell. It was cute when it was Aoko and Kaito as well as Shinichi and Ran. Then when we had Heiji and Kazuha it was a little expected and their cuteness kinda made up for it. Then it was Eri and Kogoro. Then Agasa and Fuase. Then Shiratori and Kobayashi, and by now it's starting to border on parody. And then it becomes Chiba and Naeko, fully completing the self-parody. And let's not forget the bunches of times that Gosho has inserted characters who have been in love in each other since childhood into his cases, the minor characters meant for that case and nothing more. Let's be real here, that's a little cuckoo for Cocoa Puffs. And hell, even in Yaiba, that counts as a childhood love story.
And it's funny because with Haibara you'd think that the other stereotype would be prevalent (bringing up my semi-quoted main point: "a tsundere who warms their heart for the main protagonist is more stereotypical than a childhood love story") but he actually shuts that stereotype down, tenfold no less, with an overabundance of childhood love stories. I'm a fan of childhood love pairings as much as most folks but it's like, good lord, where do you draw the line?
I don't read comic books to have an accurate portrayal of life either, but it sure did get boring in The Secret Invasion story-arc where it was nothing but Skrulls over at Marvel a few years back, didn't it?
RE: The Black Demon:
At the same time though, the non-childhood couples are also unbalanced. Takagi x Sato received most of the focusing while we don't really know what would happen to Sonoko x Makoto.
Yeah, but I feel like this is kinda the point. Sonoko and Makoto are a long distance relationship due to his tournaments overseas, hence Gosho is trying to make it so that when Makoto does do something for Sonoko, it's a little more special. The problem here is that the series is just so long that it feels like the gaps for Makoto and Sonoko are a lot longer than you'd think. And it makes it a lot less special.