Also, high-level research projects push the state-of-the-art in the private sector. When CERN order up a new type of magnet, that contract goes to a company who does magnet winding who in turn usually revamp their entire process as part of the collaboration to achieve the desired field strength, homogeneity and size.

Suddenly, there's now a company which can do that - and is eager to sell the service on since they now have the capability. Not only do subsequent magnets get cheaper, but things which weren't feasible due to their smaller scale but precise requirements suddenly become possible.

I'm not arguing against investment in big science and R&D, I'm arguing against it as a form of stimulus spending.

...in the context of fusion power...which is big science and R&D. So you're making an implied judgement there.