Can they be as good as who has CS degree?
Yes. Next question? ;)
CS degrees provide a structured and comprehensive way to learn, with plenty of time to get through it over a few years. But there are some tradeoffs and caveats:
Being self taught doesn't guarantee you avoid those pitfalls either, but it's pretty neutral. You can certainly learn development on your own, it's become much easier over the years with an abundance of online courses (free and paid). One thing you can know though, is if someone had the passion and drive to teach themselves they're pretty motivated.
I think short, intensive training has become popular because it sits somewhere in between - you're not on your own, but you also aren't paying for an entire degree.
I've hired plenty of self-taught people over the years, and some of the absolute best I've worked with didn't have any relevant university qualification at all. Some others did. YMMV, naturally.