US Immigration Comparisons

One non-obvious factor is family immigration. US is often more generous wrt relatives that you may sponsor once you're a citizen yourself, and especially on how many visas are issued in the family category (indeed, there are no caps or quotas on immediate relatives!), while other places tend to strongly favor the skilled worker and investor categories. For example, in Canada, family-based applications account for ~25% of all permanent residence permits issued yearly, while ~50% is economic;

US immigration policy isn't perfect, but it's far more liberal than most countries I know of. And I haven't looked at the numbers to verify this, but my general sense of the world would lead me to believe that the US gets a lot more applicants than any other single country, which makes its situation more difficult than theirs.

The world isn't the US, the US is literally 100% immigration

Canada has a “points-based” immigration system - you get points for various factors (university degrees, in-demand skills, etc), and anyone who gets over the cutoff can immigrate permanently. A lot easier to navigate and understand than the US rules. Hence, on a per capita basis, its immigration rate is 2-3 times that of the US.Australia and New Zealand are other countries with a points-based system. Australia likewise has much higher immigration than US, although currently not quite as high

To make that useful to the question you may want to show that this is different than in US, which sees also a lot of immigration. I added a comment that shows the numbers are also quite normal in UK and France. That should also be accounted for.

Lots of first world countries take in more immigrants per capita than the US

Many countries have quite strict limitations on immigration for work. Many countries do not permit any immigration without visa sponsorship. The U.S. permits sponsored immigration with a quite reasonable bar (e.g: H1B, L-1). Many countries have similar lottery systems, quotas and minimum salary requirements. Given the demand for immigration into the U.S., it's not too surprising to see the limits (and restrictions) be more prominent.

It's pretty accurate if you consider immigration overall, and for one simple reason: US has the most extensive family immigration eligibility, at least among developed countries. In Canada, for example, you can't sponsor your grandparents for permanent residence; but in US, you can. This is also why US is the only developed country dominated by family rather than skilled immigration, by the way.

The US allows more immigrants than any other country. What exactly is the criticism?

The US is a top immigrant country because it isn't bombing itself, and there is still the perception that one can go from nothing to something - but that barn door is closing, for sure.