Bro, Japan has plan for a 2nm RD fab to be ready by 2025. This plan is already in progress.
And Japan's semiconductor capability is in fact better than SMIC's. Micron Japan (formerly Elpida) is making DRAM D1a/D1b node with overall capacity >100K wpm. Even though comparing logic and DRAM is like comparing apples & oranges, considering the minimum feature size and the patterning complexity, D1a/D1b are considered to be about equivalent to 5nm logic.
The capability to fab chips at this level of dimension, control the defect density to enable high volume production of 100K wpm would put them ahead of SMIC.
Whether Japan has a 7nm logic/foundry fab is a business decision that, like you said, involves consideration of market demand, competitiveness, etc. But don't let this confuse this to mean Japan is inferior in technical capability.
With the global geopolitical tension looming, if and when motivated, Japan will easily surpass China. This is especially true when we face restrictions while they don't. I had previously voiced my concern about the gap growing bigger vs. the world. Until domestic immersion and EUV scanner is available on a massive scale, I still believe my concerns are likely to happen.