I've got both the K-70 and the KP. For most "normal" photographic work I don't notice any image quality difference.
The KP was bought as an a/f upgrade to the K-70 and from this perspective it works well. The extra focus-points make it easier to track a moving subject, especially with the latest firmware.
The KP does have a higher ISO capability, but you'll need to be a fan of grainy images to take advantage of it. If you're one of those users who never goes above ISO 3200 because of the noise you'll see no advantage.
I've not (yet) made use of the electronic-shutter-only 1/24000sec shutter speed.
Both cameras use the same battery. The K-70 does seem to have a slightly longer battery life. For the cost of a spare battery in my pocket this was never an issue. I bought a battery grip for my K-5 and have hardly used it. It simply makes the camera too bulky for my taste. I'm totally used to working with a camera at 90 degrees and don't consider this to be a problem.
The ergonomics of the KP are slightly different to all my other Pentax cameras, the positioning of the shutter button being particularly noticeable. Something I got used to, but it took time.
My KP is now in "semi-retirement", having been superceded for most field-work by a K-3iii.
The K-70, with it's fully articulated screen, is so much easier to use for macro-work and high-angle astrophotography on a tripod.
Just my tuppence worth, inevitably your criteria will be different and "your mileage may vary" - enjoy