When you don't know something you can start typing keywords and see what Xcode autocompletes for and read the explanation about that function from the documentation that is provided to you right there. It's not perfect, sometimes there's no documentation but it's not a big deal as you can look into source files or try it out to see how it behaves.
The basic language API is not that large, the benefit of autocomplete discovery comes when you have autocomplete on custom types of a specific framework accompanied with proper documentation.
You seem intent on dismissing something you obviously haven’t tried in the past couple years; next time I’d suggest a simple “I don’t like it” instead to save us all time.
Might not be to everyone’s tastes but it feels like a solid tool to me.