I think with Blake, someone (not sure if it was JT or Erica or whoever) wanted to make the character completely different from any other previous female agent. They succeeded, but not in a good way. I liked that she was a calming presence, but she often came off as bland and boring. And I do blame all of that on the writers.
We don't know what they're going to do with JLH's character, but unless they give us some insight into her character and qualifications early one, they'll run the risk of backlash against her. With Prentiss we learned right away that her mother was a diplomat and she'd been in the agency for 10 years. Then in the second episode, her first full episode, we learned that she was fluent in Arabic and had lived in several middle eastern countries. By her 3rd episode we learned that she resented her mother's way of doing business. "I hate politics." She was by no means more prevalent in these episodes than any other character, but we still learned about her past, her capabilities on the job and something about her character and personality as well. We didn't get that with Blake. However, with the current writers, I don't feel we get good characterization of any of the team anymore.