You're missing the point: there shouldn't be a need to "westernize". There's nothing about European culture that makes it inherently vastly superior at technological development: just look at what China was like during Europe's middle ages. It's pretty obvious that whatever the root cause of technological development in this time period is, it isn't anything inherent to a group of people. You can say that Japan isn't going to stomp the world, but from the perspective of someone in 1444, it's equally impossible that France, a divided and poorly administered nation that barely managed to fight off the English, would, in a few hundred years, almost conquer all of Europe. The only reason history seems plausible is that it actually happened.
Medieval Euro culture wasn't great. It was the spread away from it that made them superior. Increased social and economic freedom and so forth. That's what westernize means. Historically real life nations that really called it westernizing westernized and became more powerful. They literally copied aspects of western european culture.
As far as it not being inherent to a certain group of people, are you ignorant or something? There is nothing specific about a given ethnic group certainly, but cultural differences are HUGE. Seriously. Why do you think America took off as western Europe slowed down? Cultural changes.
What slowed down the Japanese was very specific elements of medieval Japanese culture. They began to become more powerful as they westernized, in real life that is what Japan did. And much later than 1444. The same thing happened to Russia.
Its almost like you think people are saying the Chinese genome is inferior or something stupid like that when its all about cultural attitudes. China pursued a policy of isolationism and tradition around the period of this game after previously being at the forefront of naval trade.
"After Zheng He's voyages in the 15th century, the foreign policy of the Ming Dynasty in China became increasingly isolationist. Emperor Hongwu was the first to propose the policy to ban all maritime shipping in 1371.[2] The Qing Dynasty that came after the Ming often continued the latter dynasty's isolationist policies. Wokou or Japanese pirates were one of the key primary concerns, although the maritime ban was not without some control."-Wikipedia
I remember this because I did my world history project on Zheng He freshmen year of highschool. I honestly just know the Russian part because I had a big personal historical phase.
Essentially China specifically closed itself off almost exactly as the time people of Europa Universalis began.
Post below appears to have gone in way more detail on the same point.
Paradox make HISTORICAL grand strategy games and if you would to lead an eastern asian nation to world technological dominance all you have to do is make a simple fucking mod starting yourself as westernized. Problem solved.