None of this happens in isolation. If you flood a country with a torrent of migrants, everything else just doesn't continue as is with that one thing happening on the side.

For instance in Canada there was, and remains, a housing shortage. Suddenly a ridiculous amount of our economy turned to speculation on and leveraging of housing. Housing is multi-factorial and there are certainly other issues at play, but it was incredible during the height of outrageous migration when apologists would pretend this adding millions of new people that need to be housed in a short period of time was somehow not a factor (suddenly the demand in S&D didn't matter, because it was a protected topic).

I know even in my neighbourhood migrant families that bought houses they could not possibly afford -- the space was endemic with astonishing levels of fraud, and you could just make up whatever imaginary income you want -- at grossly inflated prices, and the only way they could swing it is to then move a number of international "students" in their basement, the "students" then working full time at minimum wage and often below, etc. A race to the bottom. This sort of knock-on effect happened everywhere. Brampton is basically a giant tinderbox now because it was a city built on this sort of pyramid scheme/fraud nonsense.

Investments all flooded to the same spaces[1]. Who wants to build a business or make a product when you can just make an international "college" or start another exploitative low value human trafficking operation to give points to desperate migrants looking to game the system.

Every business in Canada was competing with race to the bottom "who can hire the most migrants, many who'll actually pay for the right to work" alternatives. Increasing efficiency, automation, etc -- none of it mattered at all, because it can't possibly compete with the place flooding with migrants who'll tolerate anything and accept close to nothing in return. While similar countries were increasing efficiencies, automating, and so on, we were moving to a human trafficking economy. This is true in Canada's agricultural industry where it's like the 1940s because farmers just got accustomed to massive numbers of migrants coming and doing manual labour.

Now add that as the best of the best graduated from Canadian colleges and university, they could take a grossly underpaid job with a Canadian employer, where almost all of their coworkers will be "accept anything" migrants, and fight to pay a million dollars for some shoebox condo....or they could move elsewhere. A shocking number just decided to move elsewhere, primarily the US.

This was hugely destructive to Canada. It was a massive mistake, and we have a lost decade to show for it.

[1] So did government spending. Why do major projects, seek new export markets, etc, when you can announce GDP growth regardless, even if the GDP per capita was flat to declining. A decade when we did nothing but celebrate how wonderfully diverse and tolerant we are.