Comparing mortality rates per capita at the start of a crisis when it hasn't spread at the same time/rate in all countries isn't very illuminating (and yes we are at the start, not the middle and certainly not the end). It needs to get to a certain number of cases before it can start to spread exponentially.
After a slow start Japan now has an out of control outbreak and has just declared a state of emergency - it's probably too late to contain it in cities like Tokyo. I sincerely hope they do manage to get it under control because as you say they have an elderly population but apparently hospitals are already close to overwhelmed in Tokyo and a resurgence has happened in Hokaido.
I think New Zealand (where mask wearing is not prevalent) is also a counter-example to your thesis that mask wearing has significantly changed outcomes. Not even hard lockdowns have helped in Europe (though they probably help get it under control). Test and tracing to eliminate outbreaks in detail has definitely been the most significant factor IMO, as practiced in both in New Zealand and South Korea, and interestingly Germany - which has probably seen as many early cases as France/Italy/Spain/UK due to being at the centre of Europe but has kept this relatively under control so far without tight lockdowns and without mask wearing.
There will certainly be a lot of interesting studies after this is all over comparing mitigation measures - at the moment it is not so clear which ones work, and at which stage in outbreaks they are most useful.
So many variables. I wonder how clear things will become even in hindsight. Of course, it doesn't keep people today from being very certain and very dogmatic and very strident today about the right things to do on Twitter, Facebook, and elsewhere.
https://bgr.com/2020/03/26/coronavirus-testing-explains-germ...
It's a reasonable low-value point in the broader discussion, however it's absurd as a reference of much consequence, given the outcomes in Japan and Singapore have been nothing less than extraordinary.
Compared to the US and Europe, Japan is sitting next to Wuhan. They have the oldest large population on earth. They have 127 million people. They have a per 100k persons Covid mortality rate of 0.17 --- 1/30th that of Germany, 1/68th that of the US, 1/169th that of France.
Read that again. Japan's per capita mortality rate is 1/169th that of France. Not a typo.
Mask up accordingly.