It's not a 'serious critique', it's an avowed anglophile expressing sorrow that the UK has distanced itself from a common European project, a project that has coincided with the cessation of war among European nations - something literally without historical precedent. Correlation is not causation, but since more plausible explanations are thin on the ground, it looks like a reasonable working assumption that the European project at least contributed to the era of peace.
I think where you and I differ on the EU is that while I can see most of the faults you ascribe to it (including the Euro, but excluding your oddly personal animus against figures like Guy Verhofstadt), I am open to the possibility that the 'cuddly brotherhood of nations stuff' might have some valency, and - taking a wider view - may well be much more important than any other consideration. I am quite certain that the EU has made it easier for the European nations to speak with one voice over Ukraine, for example. I also hold out hope (albeit dim) that the EU's 'democratic deficit' may be addressed in future.
Marías's father was an anti-fascist, briefly imprisoned by the Franco regime. Marías himself spent his late adolescence and university years in Madrid under Franco. I'd imagine that if he was rose-tinted about the EU, it is not because he was muddled; rather, he knew from experience what he was talking about - the stakes are high, almost abstract, and they operate at a level where 'co-operation' trumps 'sovereignty'.
Its quite interesting that the reply that he made in the interview didn't seem to me to directly address the question that he was asked, which seemed to relate to resistance within the EU to cultural interchange with Britain?
Anyway, I have much sympathy with the considered points that you (and he) make, and I am sure that they have validity to the relative success of the European 'family' over the past 70 years. Let me make it clear; I do not see Brexit as a victory of some kind - I see it as a dismaying failure; one of diplomacy, certainly, but more importantly, of the European project itself; and we mustn't forget that Brexit encapsulated sentiments that were widespread across Europe, and I suspect remain so not far beneath the surface, where below it at all.
The sentiments that Marias expresses, though shaped by his own family's experience in Spain, are precisely those upon which the European project was founded in the post-war period - to prevent further war in Europe. To the founding fathers this took the physical form of first tying a serially expansive Germany's industrial base to that of France, and using this as a springboard for a fuller economic, and ultimately, political union. To the former evolved the EEC, a broadly successful and popular arrangement. To the latter came, often by means of sleight of hand and obfuscation, the EU, a very different and far more divisive creature, and one driven by a narrow ideological objective.
I regret that I don't see the countries of the EU as 'unified' at all, and the status-quo, such as it is, only holds through grim political determination, no small degree of doctrinairism, and the binding effect of the single currency, an artifice maintained against considerable odds both to compel members towards the objective of full political union, and to make it impossible for them to leave.
The perceived unity of the EU over Ukraine is wafer thin, if it exists at all. It will be tested, I fear to destruction in the coming months. Mercantilist Germany, hitherto the sole real beneficiary of the Euro - which it has ruthlessly gamed - has been geopolitically inept in regard of its reliance on Russian energy. Hungary refuses to stop buying Russian gas and oil, and it's government probably supports Putin. Italy wants to maintain Russian energy supplies. Poland, which has taken in vast numbers of Ukrainian refugees, is subject to a block of EU funds over internal policies with which Brussels has issues. It might reasonably be argued that the EU itself, ever eager to expand its 'sphere of influence' (technocratic rulebook) was somewhat more that merely complacent in its conduct towards Ukraine in the period leading up to Maidan, and indeed since.
The concept of a community of European nations as an
idea is beautiful. Sadly, the institutions and dogma that have been born of that idea have seriously overreached. They are now threatening to destroy the very thing that they created.