Task chairs are good if you're not spending more than 30 minutes or so at a time sitting in them. That's about how long they're comfortable for. They serve a purpose, especially in places like classrooms and libraries, to discourage people from moving in and setting up shop. I don't think they are, or ever were, meant to be comfortable. That's the job of actual office chairs, where employees will spend several hours a day.
I can't sit in task chairs anymore, for any length of time. My back simply will not allow it. I start seizing up almost as soon as I sit down in a task chair.