Boring a reader isn't a matter of the length of the writing. If a reader is bored, it's because the writing isn't engaging. Intimating someone shorter writing is more interesting is neither true nor helpful advice.

That said, there is something to be said for brevity. I read a lot of stuff here on Medium that could have been said in half or a quarter of the length. Writers also do not need to repeat the same thing interminably either; that's worse than boring – it's insulting to the intellect of the reader.