Can you name another mechanic that only happened a single time throughout the entire time period?
I'll do you one better. I'll name mechanics that never happened a single time.
1. Coalitions of 5+ members including great powers against nations with <4 provinces.
2. 15 year truces that would massively destabilize a nation to break.
3. Colonization being impossible where supplying 20000 troops is practical, even trivial.
4. Carpet conversion of religion across entire regions inside a century, with no loss to human capitol or technological progress.
5. Rebellions 2-4 times larger than the largest army a peaceful nation with the territory could possibly field, revolting for years w/o foreign support.
6. War score limitations (war score actively blocks historic peace deals in fact).
7. China starts behind Europe in tech, heck China starts behind hordes in tech.
8. 50 regiments of infantry and artillery in India in 1550, shipped straight from Europe, and nobody in Europe massacres the idiot who did it.
9. Artillery moving at the same speed as infantry with no logistic consideration on how you're moving heavy pieces whatsoever.
10. Annexing vassals reduces the rate at which one can improve his navy.
Even Wiz said straight up that he's not going to take selective history arguments seriously, and there's a good reason for that. You're essentially arguing against the viability of nations on the grounds of history in a game that actively diverges from history and has a longstanding patch history of making the game less realistic rather than more so in the name of gameplay. It's logically inconsistent and fails to hold up as a credible basis for hammering westernization.
Now, can you come up with a good gameplay reason it needs to be nerfed? The nations that need to westernize already start with such a disadvantage that no nation that does it is guaranteed to match, let alone outperform history. This is also the pre-industrial revolution timeframe where technological differences were less pronounced, so being "western" in the sense of 1700 is not the same thing as 1890.
Well this is a game based in history, so those two things are in no way equally absurd. A Western European nation becoming a world-power is infinitely more plausible than China becoming a world-power because the first one actually happened.
The ignorance is painful. Qing lasted this entire period, and the only European nation that fought it on land in a serious way lost (Russia), mostly due to supply issues with transporting troops to the eastern front before railroads were commonplace. Of course, in the game you can transport hundreds of thousands of troops across Siberia and if you micro them a bit, you can do so w/o attrition...and THAT's somehow okay while Qing westernizing to be competitive in such an ahistoric environment somehow isn't.
I'm not sure why I'm bothering though, given the nature of your first question. Only by covering your eyes can you possibly conclude that this game's basis in history is anything but extremely loose with large liberties taken.