Can an author have their own style of writing but not be very good at it?

although anything you do, whether good at it or not, you’ll always need to improve.

in terms of your question, if something is your own style, most should be naturally good at it, as that style is “your own”. Meaning you are automatically an expert at it because your the one who can do it. but I guess it’s possible to not be very good at it; but is highly unlikely.

hope this helps!