There are interesting differences between US, Chinese, and European anti-trust/anti-monopoly laws. You make a very good point that we should consider if the current legal need changing.

Definitely something is broken if Facebook can acquire not just Instagram but WhatsApp as well. One or both of those deals should have been blocked by regulators on at least one side of the Atlantic. And there's an argument to be made that Microsoft should not have been allowed to buy Skype.