Um...
Also...
Let's see... snark/sarcasm, intellect, same situation (APTX). They are similar—Shinichi's/Conan's morals and desire to get involved in things is where he differs from Shiho/Ai, though she has picked up some of the former ("You can't buy people's hearts with money") from Shinichi/Conan. Which brings me to Shinichi's/Conan's effect on other characters, in terms of his morals... Ran may be affected the most (because they've known each other 13 years), but so many other characters in the series are affected, as well—Shiho/Ai, the Detective Boys, Heiji, so many of the culprits, including Vermouth. Ran being affected by Shinichi is not something that only happens to her.
You're right—the two poles aren't the only personality types... there's them, and then everything in between. I was just using sharks and dolphins as an example—an example that Shiho/Ai, herself, uses.
Eh, no...
This is what we call a case of things that happen on screen that we, the observers of said fiction, don't see—they did make friends, from age 4 to age 16-17... we just didn't see it, because this is a mystery series, and, typically, their friends from school have nothing to do with cases. We do see their friends from high school, when it has to do with the current case, but they aren't shown most of the time, because, typically, their school has nothing to do with any cases. I certainly wouldn't mind if they interacted with these friends, even if it was just so that this accusation of "they have no friends" and "they have no good friends" would cease. Do we see Heiji's/Kazuha's friends? Kaito's/Aoko's/Akako's/Suguru's friends? Shiho/Ai's friends? No—and unless they're important to a case (or a heist, in MK's case), we won't be seeing them. Again, I certainly wouldn't mind if they interacted with these friends, even if it was just so that this accusation of "they have no friends" and "they have no good friends" would cease, and that goes for all the teenage characters.
Oh, yes... one two-day adventure in three years (just under 1000 days)... so indicative.
They're already connected by the fact that three of their parents know each other... and speaking of which, Kogoro, in spite of being a gambling, alcoholic womanizer, has similar morals to Shinichi (see Kogoro's class reunion case, Kogoro's choice). His negative qualities haven't rubbed off on Ran, but his positive ones seem to have. Ran was the only one who stood up to Shinichi during his first ever deduction, and wasn't impressed. That, and the fact that Shinichi saw her being bullied, was what brought them together, initially.
I'll say it, again—the fact that Ran is kind-hearted and good is the reason he loves her, and also because she's "strong-willed and stubborn" (175). It certainly would help if Shinichi/Conan articulated why he loves her, but I can tell it's because of these reasons.
And it's true that while Shinichi loves Ran, he doesn't trust her—that's a problem. Her finding out would do quite a bit for character development, and to resolve this issue.
Now, then... I have to ask, have you seen the latest file (925), the raws of which came out, yesterday? What do you think?