First, let me apologize as I’m doing this write up from my phone on break. When I get back home, if you are interested, I should be able to guide you towards some reading.

Second, you have asked a few questions pertaining to two very distinct time periods. My formal training is in Premodern Japan. While I might make brief comments about Meiji here, I would differ immediately to those better qualified to give input there. Most academics tend to specialize and, while I can give some insights into Meiji, what I offer is more akin to educated speculation than information informed by a depth and breadth of research.

Your first question is in regard to Japanese culture. To be frank, there really is not anything “special” about Japanese culture in the sense it allowed them to adapt foreign concepts to meet their own needs. Diffusion and appropriation of foreign ideas, religions, and concepts is not at all unique to Japan. The Greeks and the Romans are a pretty famous example of this.

In popular Japanese histories you sometimes get the idea pedaled that Japanese culture is a super special, unique thing which is the root of all the nation’s success. Even in modern Japan, many an average Japanese person will attribute all that is good about to Japan to its “unique” culture. Remember, however, the question you have asked is about two very distinct time periods. To quote Japanese historian Amino Yoshihiko: “The modern Japanese person has more in common with an American than they do with their 12th century ancestors.” There is much truth to this statement. While there was a Japanese culture in both periods, these were very different cultures. In other words, there really is not a single thread that runs through the culture across time that allows for their societal leaps.

Perhaps a better way to frame it is instead why the Japanese saw such endeavors as necessary and worth the effort. I think you would find the reasons are more about international politics than domestic culture. If there is something “special” to be found it is likely in the holes of the culture rather than what it had prior to the imports. Chinese culture, for example, simply offered the Japanese too many things they didn’t have: a religion with an afterlife, a writing system, political and philosophical treaties, etc. All of these things were not only invaluable within Japan, but also gave the polity the means by which to legitimize itself on the global stage (mostly referring to China here).

Your second question is why power was not seized from the emperor. In the premodern era it, for the most part, was. It is a broad brush to paint as there are exceptions to the rule and some sticky politics, but for sake of brevity I’ll just say the elites did take power from the emperor. While it did not reach its peak in the 600’s, the seeds of certain political families ruling the court were taking place. Eventually, the Fujiwara clan would essentially rule through the emperor.

It’s difficult to equate the Fujiwara’s rise to the foreign imports precisely. Having said that, Confucian rhetoric certainly played a role. It might further be argued that Buddhist influence also weakened the seat of the emperor. Buddhist influence certainly appears to be a primary factor in why (to this day) there are no more empresses. There are a million little things that could be delved into here. The core point is that foreign imports—adapted to Japanese needs—offered intellectual, political, and cultural tools to influential clans which they used to grip power.

I know I left a lot of loose ends in this response. It has more to do with my own time being short, but if you want to me to answer any questions for you, I would be happy to do so. If you also have a specific area within all this you are interested in, I can try to direct you to some appropriate literature on the topic.

Hope this helps.