The peak for population movement globally was probably after WW II. Partition of India alone is like 20 million people migrating in 1947. Europe was almost as bad with tens of millions of people suddenly on the wrong side of redrawn borders.
Similarly here in Canada our immigration levels per capita which are very high - maybe too high - are still at a rate similar to that of most of the late 19th century.
So I am not actually sure that assertion is true.
Per capita is often a really dishonest framing
Especially compared to dates 100+ years ago, when we probably didn't have super accurate census numbers. Especially since Canadian census at the time probably didn't even really include Native Americans.
It's also very different to be welcoming large amounts of immigrants of very similar cultures, versus large amounts of immigrants with very different cultures
In my lifetime Canada is going to see enough of a demographic shift that people sharing the culture I grew up with are going to be the minority. I've already seen that many neighborhoods in Calgary do not really participate in Halloween anymore, for instance. Every parent in my neighborhood says they take their kids elsewhere for Halloween to go door to door because our neighborhood doesn't have many houses that participate
Is that a big problem? No probably not, but it kinda sucks to see
Also the first thing that comes to mind for many people when they think "migrant" will partly be those post-WW2 migrants you are speaking of (even if now in second or third generation). The migration events you mention are very fresh, especially in people's minds.
Until very recently, the first thing that came to any German's mind when migration was mentioned would have likely been a Turk (migrating here after WW2). Only recently Syrians and Ukrainians started warring for that headspace.
- "The left" will try to deceive and deny reality even in the face of hard numbers. Obviously way more people migrate nowadays than historically. Most of the historic migration was also between geographically close, similar cultures.
- "The left" is elitist, paternalizing, and kind of cringe. Academic sounding writing and quoting philosophers that have been dead for over 2000 years will not exactly endear you.
- "The left" is out of touch and will talk about anything rather than address the problems people actually face. People struggle to afford rent, struggle to maintain their standard of living, and are worried about their income and crime. This article is comically far removed from addressing that.