Rob is spot-on.
The blog (on your own domain) is your own virtual real estate. You own it, and you control it. If you want to shift to a new social media platform, you can do so without any serious repercussions.
But if you built your business on a social platform, and the popularity of that platform dwindles...
So does your business.
Having your own blog is like having a shop, and owning the building it is in as well.
Building a business on social media is like having a stall at the flea market. If it is run correctly, it can be lucrative - but if the flea market goes down, there is nothing you can do to fix it.
At least with your own blog, if something goes wrong, you can try to fix it or improve it.
That doesn't mean you shouldn't put some effort into building a solid following on social media - on the contrary. You need that solid following to drive traffic to your blog.
(and it helps with branding too)
But in the end, social media is a means to an end. It is just one thing you do to promote your blog.
Lastly, remember this:
On social media, your posts have a relatively short life span.
On your blog, your posts can get traffic from Google for years after you published them.
Your choice.