There are a lot of good points here. There are also a lot of common misconceptions, however.
Social media, just as the internet in general, isn’t inherently bad. I don’t think you were trying to say that it is, but your argument did skew in that direction. It’s just like anything else. If you overuse it, become obsessed, start dreaming in feeds, it’s taken over your life and taken away a part of who you are. But using the internet for entertainment, I’d argue, is a huge improvement on what we had previously.
People have always been in love with screens. We can see this starting back when televisions first made their appearance in every living room across the country. As an alternative to TV, the active engagement on the internet is hugely preferable. Regardless of the content of that engagement, anything that requires response or encourages interaction is going to be better for your brain than sitting entranced, watching the colors move on a screen.
With any technological advancement, there are going to be pitfalls. But within social media, there is so much opportunity that the pitfalls are actually fairly minimal. As with anything, abusing technology is a personal choice and it only hurts you personally.