Well, I'm a writer, and in actual fact, I can definitely write characters better than most people. At the same time, I can also write dialogue much better than most people. This doesn't mean I'm a better writer than everyone else, just that I'm better than many others at those two things. I sure as hell can't write descriptively (which is why I stick mainly now to play scripts/screenplays).
The thing is, I have plenty of free time, so I come up with characters, and spend a lot of time developing them in my own head. Personality traits, quirks, backstories, physical descriptions, everything. I actually have a small pool of about five 'stock characters' who I've spent the most time working on in my head, who I use traits from most often when necessary (although I can't stick to a character name for one of them, she started as Emma then changed to Abigail, then Violet, and now Hollie, Io knows what it'll be next...). That means my characters are pretty damn believable, and I don't need to worry about it.
As for dialogue, I have a weird quirk that I imagine conversations in my head when bored, or when considering what characters would say, and I try and make up little monologues or dialogues in my head between characters. Every time I write a story or script, I imagine the entire story in my head playing out like a short film, which gives me scope to make up realistic improvised dialogue (like you would in real life) there and then, and then write it down. I've been praised for my dialogue writing in several short stories, so I'd say that's one of my better skills.
The thing is, writing is a skill anyone can pick up, but there are plenty of different aspects and few people will be good at them all. For example, I'll give credit to Stephanie Meyer that she can at least do conversations well in her books. She's not a good writer, but she does have skill at writing dialogue. And someone like Tolkien, while not as engaging a writer as many others, had a very good knack for writing descriptive prose that makes you feel more in tune with the world he creates. Even if there was the odd plot hole in his stories (cough*Eagles*cough). At the end of the day, a good writer doesn't need to be an expert at all parts of the trade, as long as they can write something people will enjoy reading. That's all you need, really.
