Overall, seeing what we currently have available, the K1/K1II as compared to a number of somewhat recent offerings from Canon, Nikon and Sony, the "dated" K1 has essentially held its own across the last 5 years pretty well. Even against higher pixel count and "new" technologies, in terms of image quality Pentax is not doing so badly.
In terms of apples to apples comparisons, there are really very few consistent comparisons available. I do have to say, Cameraville up to the point where he sold his K1, did provide some reasonable comparisons.
Canon R5 vs Nikon Z7 vs Pentax K1- Comparison | Image Quality
Nikon D810 vs Sony A7r vs Pentax K1 | Battle of 36 mp camera
Sony A7rIII vs Pentax K1 vs Nikon D850 Image Sensor Quality Test - Real World Test
Nikon Z6 II Vs Canon RP | Image Quality Test
This does not address the recent Panasonic full frame - but for the main competitors, it's a reasonable list.
The question is where does Pentax take us from here - what features and capabilities, using what technology - using what sensors, providing what specific end results. So far, they have been slow, but have produced products that for the most part have stood the test of time. You have give Pentax credit for making some pretty reasonable strategic selections, along with tactical choices that still are pretty competitive.
I would suspect that Pentax will continue to make intelligent choices for the product line in to the future.