The models look fine to me. I think you're too use to seeing fat people. Most of them look average size and some look fit.

thin people exist too

I don't see anything wrong with the current models used by the iconic, most of them look like a standard size 8 to me. I think people are too used to seeing very large people so they seem thin. Some brands use their own models though and a few I've seen are relatively thin.

They’re not as thin as the Zara models! They are stick insects. But I agree, it’s depressing.