You don't need a huge navy to battle Russia. It's navy is pretty small (they don't even have a functioning aircraft carrier) and there is anyway a land connection between Europe and Russia.

For fighters I don't think 5th gen is the magic number, you can do well against Russia with more 4th gen, and the generation counter is pretty imprecise anyway, rafale and Gripen are continuously modernized with new software and electronic warfare

Europe has Aster which is a replacement for patriot with similar characteristics. Since the technology exists it should be a small thing to scale up production.

And ammunition has been scaled up since 2022 and every shell used in Ukraina is a shell that does not need to be used in the rest of the countries.