The GDPR does remove variation between countries, before the GDPR each of the 28 member states would have had their own data protection laws and while you would

The GDPR does remove variation between countries, before the GDPR each of the 28 member states would have had their own data protection laws and while you wouldn't have had to comply with all of them the only law you generally have to comply with under the GDPR is... the GDPR, plus or minus some minor opt-in or opt-outs that some member states may choose. It's one piece of legislation that is a hell of a lot more navigable and accessible than 28 different pieces of legislation. What the poster above is lamenting over is that each member state is in charge of their own investigatory authority, and this makes a lot of sense, if you have a data leak that affects only Spanish citizens you wouldn't want the investigation being carried out by a country like Sweden or even by the EU itself. However if a data leak affects multiple member state citizens each of those member states are invited to and can enter a joint investigation. The issue they believe is that France may have a stricter interpretation of the law than a country like Poland which may make cooperating with the law more difficult as you don't know how strict to be, and while this certainly is going to be the case it's not so different from any other facet of life - In the US you may favour a certain state to be prosecuted in, you may prefer to have a different prosecutor or judge, etc.