Mark44 said:
And the smaller political subdivisions mean that the constituents are much closer to the politicians who represent them.
I can empathize with the UK farmers who struggled with the mountains of regulations that came from the faceless bureaucrats in Brussels. Furthermore, the EU Constitution is problematic, both in its length and its complexity. Per this article,
https://www.cato.org/publications/commentary/hard-look-european-constitution, the EU constitution is 70,000 words, or 15 times as long as the US Constitution, which fits in a small booklet that can easily fit in one's shirt pocket. The complexity arises in its murky delineation of powers vested in the Union versus those of the individual countries. Quoting from the EU Constitution, it also states that
From the linked article, "That sentence suggests that Brussels might exercise some competence outside its exclusive authority if some undefined body decides that the EU could do it better than a member state."
For information, the principle you quote here is known as '
subsidiarity'. There had been indeed objections to what was perceived as an arrogation of powers to 'Brussels'.
You cannot contest that there are perfectly good reasons for tackling many problems at the level of the European Union. Climate and other environmental issues for instance or fisheries. Climate does not stop at national barriers, nor do fish. Talking about fish, in today's world individual European countries are little fish in the field of trade agreements, currency, and indeed foreign and defence policy - and science. It makes sense that it can act as a Union in such fields and a long list of others. In some of these fields it has been undoubted success story e.g. trade and science. (though of course as soon as you say anything like that there is somebody who comes along to say they object to this thing, that thing is not perfect, the other thing was done wrong. Apparently when you run the affairs of whole continent some things are not perfect, or at least not everybody agrees they are. Whaddayaknow?)
Anyway because of these objections or fears, the principle of subsidiarity, that only things that need to be run/decided at European level and not lower level are to be so run/decided was introduced. Every piece of European legislation or regulation now contains paragraphs setting out the reasons for which European level is appropriate.Every judgement of the European Court of Justice contains a paragraph setting out why it is the competent court. (In most cases this is pretty obvious. From time to time they rule that they are not the competent court for the issue brought before them.)
We seem however to be set for explosions to take place in some of the above-mentioned fields e.g. fisheries and trade as the two sides UK and EU now square off before a a maybe final agreement in a year or so's time.
If you find the European Constitution 'murky' that may be because there isn't one! There was an attempt to create one but it did not get through referendums (your citation is previous to that) and in its place there are treaties which are indeed (and deliberately) murky for the non-lawyer. However the setup contains plenty of perfectly clear elements (well apparently!

) such as the European Charter of Rights
https://www.europarl.europa.eu/charter/pdf/text_en.pdf
I have heard before your holding up as an example the American Constitution, e.g. an article in the Economist when the EU Constitution was being discussed held up the US one as model to be followed. Johnson is saying the same thing around now (We don't need no Constitushun!). He was arguing the other day we don't need EU rules and standards on environment, maternity leave or whatever because 'ours are better than yours

'. I don't think there is a chance of persuading 27 different nationalities of legalistic-minded continentals to do without written rules, prescriptions and binding undertakings just because of Johnson's pretty face.