I’m completely for spending a minimum of 2 percent on Defense as was being agreed by NATO members. But that’s just a number. You still end up wasting an insane amount of money by developing, procuring and reinventing everything 27 times.
The problem with that is that it is blatantly untrue.
The vast majority of the European nations buy off the shelf, the only real exception being France which, after Suez, made th3 strategic decision to never rely on the USA again.
Even the UK, once a major force in designing and equipping its only forces, has hardly done so since the 1960s, it bought the F-4 and E-3, the C-130 and Chinook etc. The main tank, apart from the French is the German Leopard. The largest fighter fleet in European NATO service is the F-16.
Yes, nations combined to build the Tornado and Typhoon - but mainly as the multinational contracts provided an insurance against politicians salami slicing orders once the industrial benefits had been gained. If you want an example of that in action I’d point to the current state of UK F-35 orders…