Plus, it's easy to forget that httpie is SLOW. Sometimes when testing an API the timings are worrying, until you remember and switch over to cURL to confirm everything is right with the world.
I don't know why you are getting downvoted. That's true, starting a Python interpreter is a relatively expensive operation. There is a noticeable lag with most CLIs written in Python.
There has been some work recently to make the interpreter start faster. I hope we will see the result in Python 3.7.