Found this part interesting. I worked for a short while in fisheries in the mid to late 90s, and graded fish for Sushi. There/then fish was iced, not frozen, as soon as captured to slow their metabolism, reduce any after-effects of stress, a cut is made so they also bleed, and die faster and as peacefully as possible. They are kept long enough to allow for rigor mortis (I guess what this article refers to aging), so when it ends it results in soft, melts-in-your-mouth meat. But no, not frozen, not for the "No. 1" destined for best clients. Lesser (cheaper) restaurants yes, frozen, older, lower quality fish.

This article refers to the US, and yes most of it is far, far away from the coast, and only way is to freeze it to distribute it such long distances. Unless flown in, obviously making the product much more expensive. So sure, as title says "Most sushi fish isn't fresh". In the same way, most sushi isn't the best sushi. And in many cases it doesn't really matter, if you want a quick and still yummy meal.

For tuna you can readily tell, even if you haven't trained your sense of smell, by the color. Most tuna here in the US you can see it a matte pink, instead of deep, alive, blood-like red, and you know right away it's been frozen.

Anyway, it seems to me the article gives the idea that freshness doesn't matter at all for sushi. I disagree.