I think it's fair. Honestly I think it's such a weird phenomenon of people on the internet that they always expect stuff to either be or remain free.

A personal blog can easily run on 500mb and remain free. Just limit your image use (and use webp!) If you're a (amateur) photographer or something, and need a lot of storage space, you're either making money with your profession or you already have an expensive hobby, so what's 15$?

I wouldn't call it a betrayal. It's a business, and they're allowed to make business decisions as they see fit. I think to most people, it's more important that wordpress.com keeps existing, right? Or should it remain free/cheap and at one point just close its doors?

What I do think is interesting is the visitors cap; with only 100k visits on a premium plan it seems they're reducing their focus to relatively small sites/businesses?