I knew that it's easier for speakers of European languages to learn English than for East Asian languages, but your ability is way above what I thought would be feasible without spending insane amounts of time on English.

I probably do spend insane amounts of time on the English internet. An amount of time that a Japanese student simply couldn't because he's to busy keeping up with the extensive school curriculum in the Japan. East Asians tend to spend a lot of time to drill children to perform well on standardized tests with doesn't leave much time for things like learning English.

Another issue is that a lot of the language teaching of English in East Asia is simply highly inefficient. That will change with various internet elearning projects.

An outlier would be Singapore where as Wikipedia suggest: "The English language is now the most medium form of communication among students from primary school to university."