It's not as if Japan (or any other country, for that matter) doesn't already have immigration restrictions. Japan uses a points-based merit system for permanent residence [1], not unlike the criteria you suggested. Just to give an example, having a PhD and speaking Japanese at an N1 level (~equivalent to B2 CEFR) is barely sufficient to qualify (unless you're older than 30, in which case it won't be).

The more interesting question to ask is: Why has Japan decided to tighten immigration requirements now? But in my opinion the answer is rather obvious, especially when you consider the current Prime Minister's nationalistic beliefs: It's much easier to blame foreigners for insufficient welfare, ailing infrastructure, etc than to actually improve welfare, infrastructure, etc.

Also, the example of "a 68 year old alcoholic high school dropout with multiple violent criminal convictions" is rather ridiculous. You're arguing a strawman. It's already impossible for such a candidate to immigrate almost anywhere barring some other exceptional circumstances.

---

[1] See here, eg, to see how you would fare: https://japanprcalculator.com/