I think that autodidact developers are better than trained ones in the sense that they are more motivated. They made efforts of their own to learn the ropes, while trained ones just received input.
More motivation learning also means that those people don't only read one source, but often have to read several different sources to understand a certain something, which means they read a variety of opinions, standards and best practices. It's not only one "source of truth".
After putting all that effort into learning, such people probably also tend to be more motivated using the technologies they learned (if not for usage, why else did they learn it?). And while using it, evolving further is very natural for them. Because it's something they like doing, they will try to become better at it. It's fun to improve, actually!
Of course, there are downsides, too. But imho, in the long run, autodidact developers are more motivates which leads to a lot of bonus side-effects, so yeah, I would describe them as the better ones (and the ones I would prefer to hire)