This method is number one. I can tell you I use this method personally. I am continuing loving how this works and you will too, let me explain...
I think stopping and learning the basics (how sentences are formed and how words fit together in Western English) would definitely improve writing. Which means they should start reading more. Books, not blog posts.
I don't think long sentences make content harder to read, depending on who is writing them. Sentence length serves as part of literary structure just like short sentences, figurative language, etc. It all comes together to form an individual's writing style.
I write in long sentences because that's just my personality. I'd like to think it doesn't degrade the quality of my writing skills.