Japan is not a country open to immigration, your can spend 20 years there, speaking perfect Japanese and still be considered a complete stranger.
Anyway, it's not really Japan specific. I'm not sure why people always say this about Japan when other Asian countries have an even lower immigrant population. In Taiwan it's just over 1%. In Mainland China it's even much lower. Korea has slightly immigrants than Japan but it's no where near levels of Australia or the US. There's a weird obsession with Japan in Western countries and Japanese culture and politics often get stereotyped without people actually understanding much about it. The assumption that it's unusual for a country not to have (uncontrolled) mass immigration is in itself an amusing one to me.
Only a few thousand per year bother. There's actually hundreds of thousands of eligible long-term residents in Japan who could acquire citizenship on paper, but the criteria (particularly the renunciation of other citizenships) are burdensome enough that even some people born in Japan who have lived there their whole lives who could become citizens opt not to.
In particular, starting at 1m04s, the interviewer says "I hear it's hard to become Japanese". And the naturalized person answers, "the more and more I read about it on the English net, I realized there's so much misinformation about it that you really couldn't trust anything that was written English about naturalization."
He's talking about people like you. He spends the whole video in particular debunking almost every point you made.
More than 20% of people living in Canada are immigrants.
Immigration rates have increased since the data above.
Brazil is an interesting one, because a significant number of "Brazilians" in Japan are supposedly descendants of Japanese who had immigrated to Brazil, but then came back. But even they experience degrees of discrimination despite being ethnically Japanese.
Anecdote, but my Japanese American friend (ethnically 100% Japanese but born and raised in the US, and pretty much culturally 90%+ American) went back to Japan. He too experienced discrimination.
There is lot of pressure to conform to the generally accepted social norms.
"Gaijin" gets played up in weeby debates -- by people who are looking for reasons to be offended -- as some hugely significant cultural deviation, but it's honestly more like "foreigner" in practical usage. That word can be incredibly rude, or completely innocuous in different contexts. As can 外人. It's more accurate to say that both words mean "foreigner", but 外国人 is the PC version that renders you safe from criticism.
(The irony, of course, is that no matter where you go you'll hear plenty of borderline racist policy talk with the sweetest of language.)