Cathedral and a library on a budget

The limitation is that only one sample of a lens is reviewed. There will be some variation between samples, and reading the user comments recognises this. The WR version has the same optics as the non WR version, so should be the same, subject to any variation between individual lenses.

This is what I've always believed about the DAL lenses...

"SMC Pentax-DA L zoom lenses are optimized for use with Pentax Digital SLRs. They cannot be used on film because they only cover the APS-C image circle. The DA L series is a budget series and differs from the DA series in that its lenses do not offer quick-shift focusing and have plastic rather than metal mounts. Pentax DA L lenses are only available in camera kit bundles."

(Source:https://www.pentaxforums.com/lensreviews/SMC-Pentax-DA-L-Zoom-Lenses-c51.html)

Along with some old sandwiches curling at the edges and an ancient flask of by now cold coffee???

On a more serious note, have you tried calibrating the KP's AF for the D-Xenon? There's sample variation in both cameras and lenses. It's possible that a bit of fine focus adjustment could work wonders for that lens on that camera.

Another thing I've noticed with a 55-300mm from the same era is that AF accuracy depends on whether focus is approached from near or from far (but I can never remember which is best...). Perhaps worth checking whether your D-Xenon has the same quirk.

Steve

That looks OK to me. I owned a Pentax DA WR 50-200mm for a few years and was never very happy with the sharpness, even stopped down to f/8. I switched to taking an older M-series prime (135/3.5 or 120/2. which was smaller, faster, much sharper but of course fully manual.