Imagine running a business with a series of one-year guns pointed at your head, never knowing if they'll go off. Countries can and do summarily change the rules for work visas all the time: for example, in Singapore during COVID, the government decided to shore up local employment and score political points before an election by suddenly announcing that spouses of employees could no longer apply for work rights (Letter of Consent) and that existing LOCs would not be renewed, throwing a lot of families into disarray.
It's even worse for an unusual visa like this, where a lot is left to interpretation. You may get a different officer this year who is going to nix what the previous one allowed last year, and appeals are uncertain, cumbersome and may require you to leave the country.
Renewals in Japan are guaranteed if you meet the requirements. Japan foreign worker visa rules are very straightforward. The number one cause for concern would be if your business generates insufficient revenue to pay your a minimum salary required by the visa rules. And the minimum is rather middle class. Before you reply very quickly saying: "What if they business has a bad year?" ... please answer from the perspective of other highly advanced, wealthy nations: Do they want to allow people to stay who are running weak/failing businesses? Probably not.
> in Singapore during COVID ... suddenly announcing that spouses of employees could no longer apply for work rights
This is the reason that I never recommend to live in Singapore as a foreigner, unless you are working as a senior manager for a very large corp.
> Countries can and do summarily change the rules for work visas all the time
Not in Japan. In the last 50 years, they have universally become more liberal about allowing highly skilled people to live and work in Japan.
It's even worse for an unusual visa like this, where a lot is left to interpretation. You may get a different officer this year who is going to nix what the previous one allowed last year, and appeals are uncertain, cumbersome and may require you to leave the country.