I agree with the conclusion, but I don't think it should be done through the current antitrust framework.
Your first point and most of the others others may or may not be illegal. If they are legal, what the MPs need to do is their jobs.. make laws. But, most are not directly related to company size and/or market share.
Your second point does sound like a trust and I think you're right to link this to the WhatsApp sale.
But... Regardless of the FB/WhatsApp conclusion, that is a one-off that won't lead to much systemic change whether it's a fine or an order to de-merge.
What we need (imo) is a whole new approach to antitrust that doesn't hinge on a definition of monopoly.
Companies beyond a certain size should just be put under a different set of obligations than smaller ones. They should be assumed to have market power by merit of their size.
When it comes to gdpr and such, these need to be written differently for large companies. Basically, no more equality before the law for companies. What we get in return is rule of law.