It's just the reality of Aeroengine Industry. China has thrown a lot of money at it in the past 10 to 15 years and it is still 20 years behind GE, RR and PW. This is an industry that requires continued investment in the billions over many many years. None of the companies will disclose the real secrets that took years to build up. All new entrants need to learn things the hard way. What the Turks are saying is simply not realistic.
Maybe they will be capable of developing a domestic turboshaft that's usable on T-129 in a few years. The entrance barrier for turboshaft is a lot lower than high end turbofan engines. That's what we are talking about here. Advanced turbofan engines for the next generation fighter jet. There are a lot of companies/countries world wide that have tried to get in on aerospace engine and have not gotten close. Building a modern 4th generation fighter jet is a lot easier than building the turbofan engine for it. Building a modern 55h generation fighter jet is easier than building the turbofan engine for it. Both J-20 and Su-57 are still using upgraded versions of engines developed for 4th generation fighter jets. Just think about all the high tech countries like Japan, Korea, Israel, Germany and France. None of them can really compete with PW, RR and GE in this space. Yet, Turkey can do it in a few years.
If we step back from modern aeroengine and just focus on the "easier task" of developing 5th generation aircraft. If Turkey is capable of developing a 5th generation jet, then how come none of the countries it reached out to is interested in joining it?
State owned defence company Turkish Aerospace Industries has invited Malaysia to joint the TF-X fifth generation fighter program which is currently under development,
militarywatchmagazine.com
This is not just a shot at Turkey. Korea is attempting to do the same. It even managed to sign a deal with Indonesia
https://www.defensenews.com/global/...jet-partnership-with-indonesia-falling-apart/. And now Indonesia has basically given up on the project when it invested $10 billion on Rafale/F-15ID over the space of a week. If it's so easy to develop a 4.5 or 5th fighter jet and engine, why do all these countries with money continue to go back to purchasing the latest iteration of Western 4th generation aircraft?
This is really hard and it takes many years of heavy investment. Don't underestimate how much progress China has made to get to where it is now.