How terribly naive, thinking GDPs and budgets translate into industrial capability and the ability to build something in reality. Newsflash, the US has the biggest budget and the USN is the biggest Navy by displacement, yet they can't built a simple frigate without running multiple years behind schedule.
If one thing is synonymous with the UK military, it's complaining about funds. How do you expect a country that has to cooperate on several high profile programs to minimize cost (Trident, AUKUS, Tornado, Eurofighter, Jaguar, etc. etc.) to somehow be able to produce a cutting edge jet fighter all by themselves? GCAP is already looking rather conservative, especially compared to what the Chinese and Americans propose. If the UK would have to pay and develop everything themselves, there's no chance that the result would warrant the "next generation" label.
Can't keep their ships at sea, can't keep their submarines at sea, can't develop high quality aviation on their own since decades but is somehow capable of suddenly developing something they couldn't do at the height of the cold war. I like your sense of humor, mate.
Almost as amusing as trying to sustain a second rate military on third rate funds, ngl.