Not sure why it's a bad example. 35 years later it did not "just re-merged", it still is in a few pieces. You need to think about how the present would look like if there was no breaking up. And that present likely would not have google, fb, amazon - only AT&T.
The diagram has 3 input companies and 3 output companies, so at a surface level it seems nothing has changed. Even Google Fiber couldn’t compete with the big guys because (at least partially) these utility companies are so entrenched in lobbying etc.
I don’t doubt the break-ups are effective in the short term, but the long-term behavior in this case seems to be less affected.
