Knowledge transfer only goes so far, and often only transfers rudimentary parts of them, do you really need examples from the modern world? Japan didn't become a western power because they traded with westeners, it had to be through a difficult reform and transformation of society. The tech difference was appropiate pre-aow, the only issue being it inappropriate for different regions. Having SS-africa getting the same tech as China.........
Sure, but what does having a neighbouring Western province have to do with anything? Why is 'Western Arms Trade' a general tech bonus, rather than just a military tech bonus?
The 60% tech penalty for Korea, Japan and so on has never made sense, certainly not one that's in place from 1444 onwards.