I've got both. For me the KP was considered an a/f upgrade from the K-70, and in that respect it worked. I do a lot of wild bird photography and the KP gave me a bit more capability with a moving subject (as did the K-3iii from the KP!)
I prefer the ergonomics of the K-70 for most things, it's just so much more like my other Pentax bodies … the KP is just a little "different" in several respects.
If you "need" the a/f performance, maybe the 1/24,000sec high-speed electronic shutter appeals, or the extra 3 stops of low light sensitivity … then the KP is the camera for you, though do try to get one with all three optional grips, so you can tailor it to suit you.
Other than that, the K-70 is cheaper, has a fully articulated screen, a more powerful flash and a (slightly but noticeably) longer battery life.
Beyond that, both cameras are much of a muchness … I'd say superb, but the K-3iii is superb, so let's settle on "very good indeed"