I am not stopping a defense of the Cochrane review. It’s the best current study we have and it announces that it’s not clear if masks work. If we don’t know if they work, why should governments keep mandating them? They shouldn’t. Full stop.
Regarding Japan, here’s an article by the NYT: https://www.nytimes.com/2022/01/24/opinion/japan-covid.html?smid=nytcore-ios-share&referringSource=articleShare they talk about Japan’s success. Notice how masks do not feature heavily in the article.
Here’s another one that places your claim in doubt: https://www.cfr.org/in-brief/japan-covid-19-pandemic-response-restrictions-two-years
Finally, the total number of deaths in Japan and the US differ widely in large part because the two populations are, broadly, very different. COVID disproportionately effects overweight people. Ask anyone that worked in the hospitals during peak waves. The simple fact is that fat people don’t do well with Covid. Now ask yourself, is there an equal number of overweight people (%) in Japan to the US? No. People in Japan are far less overweight than people in the US. It’s no wonder, therefore, that the US fared worse because it’s population is move overweight.