Please explain it a bit further, perhaps some examples would help.
In the ADF context? Collins, MEKO, NH-90, and obviously Tiger for starters. I'd argue AUSteyr as well, though its not a compete fiasco. Just kind of a yesterday's news rifle.
Australian Defense procurement is driven by getting jobs for Victoria, and on the political Left, a perennial desire of showing "independence of the US." What that gets Australia is kind of amorphous, but there it is.
It is rarely about either the best solution. That's OK, as far as it goes, as the US has its multiple procurement fiascos that are complete own goals, but it does come with tremendous opportunity cost for more boutique sized users as dollars are flushed down the drain to try to make less than optimum weapons work as designed, or older but capable systems are kept in service and their life-cycles get shortened (see the S-70 in ADF service.) Americans have the luxury for now of shoveling resources at poorly executed designs like the F-35. Euros don't have that luxury, so half baked stays half baked.
As pointed out, both spiral development and product support are functions of economies of scale. Its just difficult for cashed strapped Euro countries to buy the spares, so the spares aren't bought. Comparing the product support of the Mirage III and F-18 from the perspective of the RAAF guys was apples and oranges. Low usage/high impact parts could and would be cannibalized from US stocks. and delivered via overnight freight for example, where Dassault and Eurocopter had a far more Just-In-Time view, and often the wait for spares was measured in weeks or months.
Even as far as the requirements for weapons goes, the analysis driving what the actual requirements are in the European context are FAR more nationally driven by non-military factors than in the US (for example, the A400M engine) and this has knock on effects to cost to acquire, performance and sustainment.
Honestly, I think one thing that the EU would be well advised to do for lots of their defense procurement would be to hire Americans (especially former inhabitants of the Military Industrial Complex) to act as an honest broker.
Again, look at the A400M. Its a fantastic design, if your requirements are to sustain the French defense industrial base and support French style rapid intervention operations. For other stuff, it was really less than adequate, and its performing far more poorly than its pedigree should suggest. Honestly, I had high hopes for the C-390 to break the American monopoly on defense tactical airlift (monopolies are never good) with a company that has international presence for support, an understanding of militaries that don't have unlimited resources (the American money machine goes BRRRRRR!!!) and price point that makes good enough, good enough.