I don't think that's a highly informed comment. As far as I'm aware choosing time zones has always been a member state decision, where as clock time changes have been regulated by EU in order to be uniform. Nothing changes in regards to time zone regulation. It's just a political expression to say that you can choose to be in "summer time". In reality there's no such thing as permanent summer time.

The reason why it's politically expressed this way is because there is a strong majority consensus that summer time probably isn't useful, but there's isn't one about which time zone should be used. So expressing it this way makes it easier for the politicians.