The issue is not that the EU declares it illegal to move to a low tax domicile. It is that Ireland and the Dutch have been breaking both EU and International tax laws and treaties. In other words, the countries were running a scam. This is fully described in articles I posted earlier.
The EU making all kinds of allegations that it is unfair to have lower taxes and that corporations are breaking laws and treaties is slightly different than stating that they are criminals breaking laws and running scams.
If they were really running illegal scams, the scams would have to stop like right now, wouldn't they? But instead, the deals that are currently being used are grandfathered until 2020. That should tell you something about the alleged illegality of them. The EU and the US simply do not like citizens and corporations moving to save taxes. Even after the double sandwich method is gone, people will still move to lower domocile locations, because taxes matter.