No, that's not wrong. Its just the effort toward farm raising them that counts, because it is like farm raising tigers, sharks, grizzlies or eagles for food. They are magnificent, top predators. Why they don't just eat Yellowfin for a little while, I do not know. Yellowfin can be sustainably harvested, and Bluefin(while it does have a flavor all its own), is not THAT much better that we should kill them all, like on the tv show 'Dinosaurs'.
Most frozen tuna for sushi is Yellowfin(Ahi), and when I am at the sushi bar, I like to see fresh tai and frozen tuna.