I'm more amenable to this kind of bonus TBH. Kinda like how a lot of countries bought muskets of Europeans, but Japan not only bought them, but reverse-engineered them and started making them to such an extent that during Oda Nobunaga's time, Japan was the single biggest producer of muskets, and owned a higher share of the world's muskets than any other nation on the planet. This should (and AFAIK, is) represented as bonuses in a number of Japanese idea sets and missions, and rightly so, while not applying to, say, Ming, even though Ming also engaged with Europeans.