I think one reason things blow up on Twitter has to do with with the magnification and positive feedback loop that goes on between itself and other mediums. If it were self contained the impact and general awareness would be much reduced.
It's the job of the media to report what's going on, and Twitter is at the size where something happening there is a legitimate news topic. I would agree it's probably overrepresented, as the great bulk of journalists use Twitter, and it makes many of the aspects of content-generation much easier.
At one point there was a clear distinction between "online" and "the real world". But I think that is now misleading. Online is now one important part of the real world. We won. Now we have to figure out what to do about it.
Most obviously relevant is Black Lives Matter. Police brutality and other biased policing has been happening in America since the beginning. The media have been generally happy to ignore it. (Even when they cover mob killings, it's often been with a neutral or even approving tone. [1]) BLM happened because of social media, because 300m people are now publishers and editors, not just article subjects.
Since then we've seen plenty more. If you're not on Twitter, you may not hear about these things until you see media coverage. But that doesn't mean they're not significant events, both societally or for the people involved.
[1] https://www.amazon.com/dp/B00D614D80/