Who fabs Pentax chips?

Yes, most sensor improvements since cca 2012-2013 are about on-sensor-AF, higher FPS, better video read-out.

Resolution stepped up only recently with Canon 32Mpix and Fuji 40Mpix APS-C.

Hi-ISO capability barely increased on sensor technology during last 10 years, but DNR processors are more and more powerful so they can compute digital noise reduction algorithms faster and with more iterations resulting in so-so usable ISO around 6400/12800 for smaller picture sizes. But if you want really clean image with very little noise (and noise cancelling artifacts), you are still down around ISO800 anyway even with the most modern APS-C cameras or hi-res FF (60mpix) cameras.

Yes things like K3III boast about 1.6 million ISO, but images taken with ISO25600 are barely usable for some web/instagram small pics. Although some users claim, that they like such pics, but that is different story and I understand that sometimes it is better to have something (no details, various noise, minimum dynamic range, destroyed colors) than nothing

In reality even that old K20D sensor with most modern DNR processor would do much better output than what K20D or K7 could back then. There is even a SW tool to fix magenta fragments in RAW images of K20D that simply replaces what camera processor was not able to finish during process. Or maybe it could do such algorithm, but then camera won't be capable of 3 fps, because it will take longer.

With K20D 21fps mode it is clearly visible that those pics are low-res, JPG only AND only with very limited processing. A lot of artefacts, color errors and strange SW sharpening is visible. The processor of that camera simply had no more power.

K7 improved it a bit and had PRIME II, so that camera  was capable of more FPS and even had some video options, although used basically same sensor.

And then big step forward was K5 again with PRIME II, but also with new Sony sensor and more faster memory chips.

K3 again pushed limits with PRIME III, even more memory and it was able to cope with more resolution coming from 24Mpix sensor.

K70 had PRIME IIM, KP and K1 used PRIME IV and they even had co-processors designed only for DNR work (called accelerator). K1II added another DNR routines to the table (which some people dislike, as those photos might even be overprocessed).

It is similar to how RAW development software evolves. 10 years old version of Lightroom is not as capable as current ones and if you re-develop old RAWs with new software it often looks better. More advanced noise reduction, more advanced detail and color handling. Etc.