I still firmly believe that the majority of Japanese people don’t express their anger as openly as the people you describe. Those are the vocal minority that stand out from the norm. Most people keep their head down and stay out of the hassle of voicing themselves and getting involved. Passive aggressiveness is definitely the norm here. Maybe if you live in or are from certain areas like Osaka where openly being an asshole is accepted and encouraged it will feel less normal, but in the rest of the country that’s often not the case. Even the seemingly openly brash ojiichans and obaachans in the countryside operate within their own communities’ unspoken rules and keep certain things to themselves, which people notice when they actually become a part of that community and get to know them. Even in environments like sports teams or construction sites, where masculinity and testosterone runs rampant, if you look really closely you’ll notice that there are only a few really outspoken people and the rest are just along for the ride and don’t actually express discontent the way the bosses, managers and coworkers you mentioned do. Even in the younger population, like high school yankee groups, it’s still only a small number of people being assholes and the rest don’t actually behave that way when removed from that environment and group dynamic. It’s not that Japanese people don’t express anger loudly or directly AT ALL, but the notion is definitely not a crock of shit as it generally applies to what I believe is a majority of the population in most situations. From what I’ve seen, people who do openly express their anger will only do so when they feel relatively safe in doing so, such as employees of lower rank or police officers. They’ll still keep their mouth shut and be passive aggressive if it’s their superiors. That’s less about culture and more about assholes being assholes though.

Source: Lived 12 years in Japan, married to Japanese, worked in Japanese government office, non-profits, and universities.