It’s easy to dogpile. I’d like to see more proof, that’s all. “It’s obvious” doesn’t cut it for me. For one, we have major societal problems that are being exposed through these platforms, and the mere knowledge of the problem has a negative impact on the individual. Do we shut the platform down because it’s showing us things we don’t want to see, or do we fix the societal problem? And many others.
It varies by demographic, but yeah, social media are pretty universally awful for humans, and that's not just conjecture.
That's the issue, and it is what you attempted to answer.
Causation is much harder to tease out from the noise.