Sure, designing modern integrated circuits isn't easy. However it still is way easier than what you need to manufacture them. Design of digital integrated circuits is commonly more understood with information being readily available.
In theory you could gain the knowledge to design an early 1990s CPU at the logic gate level by reading some books and doing a bit of research, on the other hand actually manufacturing such IC would take considerably more effort.
CPU design has come a long way since the 1990s. Superscalar designs, high speed memory interfaces, multi-level caches, out-of-order execution, machine level translation, JIT optimization, the list goes on. Just one feature of frontier high performance chip design is far more complex than an entire MPU from decades ago. And many of these techniques are IP protected. Which is of no concern to China. But here in the US it's a big reason why there hasn't been as much competition in this space, aside from the ISA cross-licensing agreements of course.
Design and manufacturing are both engineering problems. Throw enough people and money at the problem and it will get done eventually. What we're banking on in the West is by the time China catches up to where we are now we'll be on to the next thing. Always one step ahead. What I'm saying is, unless we refocus our society on STEM, those days are numbered.
In theory you could gain the knowledge to design an early 1990s CPU at the logic gate level by reading some books and doing a bit of research, on the other hand actually manufacturing such IC would take considerably more effort.