[Xixi]

In your example if Ireland Co makes 30% of its sales in France, then it would have to pay taxes on 30% of its profit to France (at French rate). That limits the reason to go to Ireland in the first place, which is why Ireland is largely against it. In fact it would encourage corporations to move their costs to countries with large customer base and high taxation rates to reduce the profits there, so it would favor the like of France, Germany or Italy.

The "trick", if I understand, is to only care where the final service/product is actually delivered. So in your example the idea would be to ignore France SAS, or rather I imagine to assume Ireland Co and France SAS are one and the same, and tax them "together".

At first glance it sounds very hard to setup (and it certainly is), but that's what is being attempted here. On the other hand it's not particularly complicated to know whom Google is selling ads to, and where iPhones are sold, so there must exist a solution to this problem...