Google has apparently put considerable effort into making touch sensitivity excellent, and they claim they have measured touch response faster than an iPhone or Samsung.
I've never had a phone in my life that had different touch sensitivity on different areas of the screen - to me it sounds like your specific 5X has a screen issue.
I can tell you that on my Pixel XL general speed/touch responsiveness is as fast as anything I've ever used and the screen responds exactly the same all over.