Correct me if I am wrong, but most of these services, such as the electronic signature, the electronic seals and the document exchange functionality outlined on that website are all dependent on a central authority are they not?

Your signature certificate is issued by your government (or an organisation working for said government). The seals are created with certificates that are, once again, created by a central authority.

The document exchange is really just a fancy way to store files on your device and send them.

As far as I can tell none of this is decentralised? I don't really see why they would want to decentralise it either, your digital identity as a citizen only exists because a central authority, a nation in this case, validated you to be a citizen ...

As mentioned, correct me if I am wrong, but as far as I can see all of these EU plans are basically just giving each EU citizen a cert that is issued by their government and some nice applications that build around those certs?