Under the terms of the PPP the DB scheme cannot be closed to present members except by NATS closing down unless those members agree to it. That is my understanding anyway.
The reason the RA is so good is that if you are a controller, especially in area, and you were made redundant where else could you work? Nowhere in the UK and could be tricky abroad as well as licenses have still not harmonized. Therefore it is a big commitment to work this job despite the relatively good salary. It has no real skills that could transfer to another job so it is expensive to try and provide protection to staff. Comparing to pilots is wrong as if you have a type rating in a 737 you can work in almost any airline in the world and just need a short course to get up to speed on SOPs. ATCOs either need to revalidate somewhere or completely retrain and then revalidate, which is why most countries don't poach ATCOs as it generally is cheaper to start from younger people on lower starting salaries.
Just some thoughts.