If you zoom out, it's not especially concerning.

The history of media companies suggests all of these companies will become less influential in little time. A few people used to own radio stations. Then it was TV stations. Overlapping them was newspapers/magazines. Things come and go, they tend to concentrate power, but they don't seem to last very long. Facebook, Twitter, Instagram and Youtube are young. There is little indication they'll have much influence in 20 years.