This is what they want you to believe, sure, it will help in the short-term. But when switching, losing most of them, and losing your content (if not moved with you), but all the domain ranking, is much bigger. And the real discovery happens on social media or through writing high-quality content that will always be shared or discovered. But all of this applies to blogging, newsletters only, like sending your thoughts via email, is OK, but a real blog, I'd want on my own domain/website.