Facebook would like you to believe that everything just happens on FB and you don't need any content outside of the FB eco system. I can absolutely tell you that's not the case. There are hundreds of thousands of people putting stuff up on instagram / FB and that does not make them influencers. If your goal is to become a blogger then you need a blog :) If your goal is just to become some sort of an influencer, then you can become one on any of the SocialMedia platforms and you don't really need a blog, but in my opinion, when you have your own blog you free yourself from any one medium as you actually own the content, the way it's displayed and where it will be featured. To summarize, I would always start with good content and you might as well get a blog. There is no down side.