The problem I have with Warren's proposal is that I don't believe existing antitrust law addresses the current problems comprehensively. Distortion of markets is only one part, albeit an important one. But privacy is another. The Sherman and Clayton antitrust acts are over 100 years old, and certainly never anticipated appropriation and exploitation of personal information as a business model. If you are concerned with privacy (as I am), forcing Facebook to spin-off Instagram, WhatsApp and Messenger will not make much difference as long as it's legal for data brokers to aggregate your data from all of those sources (and others) and sell your profile without your knowledge or consent.
Ever since I read The Age of Surveillance Capitalism, I've become convinced that new legislation is needed. Big tech firms can rightly argue that their spying is not against the law, but that's because the needed laws have not been enacted yet. The EU has made a timid start with the GDPR, but governments face a daunting task getting ahead of the privacy challenge, as corporations are far more nimble. In the meantime, I don't think it's a bad idea to subject Amazon, Google and others to scrutiny under existing laws. Just don't expect miracles.