They don't want to risk someone coming for a job, getting fired and becoming a drain on the social safety net. Able to care for themselves not just now, but for a while. It's a reasonable position.

That’s the case for every western country, and none ask for enough money to cover 30y of life. That’s way, way above the goal you mention

Reasonable, but they're going about it in irrational ways. For example, a person on a student visa is allowed to set up a company in Japan, but technically they're not allowed to put in any hours managing it. There's a strict 28-hour/week working limit, and a person is allowed to operate as a sole trader performing very specific tass, but the moment they rent an office or hire an employee they're in violation of their visa.

So while it's very rational to demand strong language skills, and very rational to expect people to go with a certified school given the unique difficulty of the language, potential residents are essentially limited to earning part-time wages (typically much lower than full time) during that period, and virtually barred from proactively engaging in any other kind of economic activity. They could transition to a business manager visa after that, but it will have to be a new business set up from scratch which must include at least one Japanese hire as well as minimum language skills; essentially requiring business activity/know how and business planning which the person was barred from doing during the language acquisition phase.

It's not impossible to meet these criteria by any means, but it actively discourages bootstrapping and efficient use of available time.

To qualify to long term residence means that they worked for years and contributed with taxes during that period, so it’s only fair that they get protection in case they happen to lose their jobs.

For the government, the cost for any worker in the same circumstances would be the same. On the other side, the foreigners cost less to the government overall when they were educated and raised elsewhere.

I’m not saying you are wrong, just that the previous rules are already in place in that very direction, and the changes are being placed instead to please and gain political support.

If they can't find a new job in 30 years then there are larger problems.

That's not how good risk analysis works. You also have to consider the alternative that you exclude someone coming for a job they excel at while becoming a net benefit to society just because they couldn't support themselves in an eventuality that didn't come to pass.