Many of these China economic collapse articles came out during the 2015-2016 Chinese stock market crash. Many used superficial research with questionable logic. There were some hedge funds who bet against China and got slaughtered. There are plenty of corpses in the industry due to this misjudgement. A lot of it was driven by wishful thinking and misdiagnosis. Chinese economy does have its difficulties but not what these "experts" think it is.
I don't believe China is a challenge to USA yet, there is so much ground work to be done but it is no where near the fragility some pundits suppose it to be, it shows their lack of awareness. Actually the more external pressure is applied on China the faster it develops technology and the greater the internal cohesion.
Japan isn't able to be competitive in a broad range of technologies due to its economic scale (limited by current technology). It is also not as economically vibrant as many tout it to be, though still a nice place to have a vacation.
I can empathise with those who say Japan will be the most powerful nation of Asia and not China since they feel much more familiar and at ease with Japan (anime, cameras, cars, VCR, etc.). China for some goes against their world view. Such views are understandable but betting your investments against China is not recommended. Videos like this just plays into wishful thinking:
Outside of geopolitics and recent history many Chinese actually like Japan and Japanese people. It is just that East Asians tend to sound critical much of the time, we don't have that much hate but just sound critical. To be honest China doesn't fear Japan all that much, it is not because Japan isn't strong but China understands the dynamics behind Japan's actions.
17 of the 32 major hotels around Mount Fuji are owned by Chinese.
Japanese drama about Japanese real estate agents selling to Chinese buyers:
