In the past big monopolies have been dismantled. See for example AT&T. Google, Facebook, Amazon, they exist for a relatively short period of time. Don't you think they will also be dismantled in the next 10-30 years?
See the diagram: https://www.theverge.com/2016/10/24/13389592/att-time-warner...
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.