My perspective......
I am not a Pro shooter or anywhere close. Silly as it sounds I shoot the K1 in Crop Mode 90% of the time. For what I do I don't want or need large files.
Wildlife is best suited for the crop shooting and it cuts down processing time considerably.
What's better....
*For still shooting the K1 AF is excellent, fast, and accurate. Best of any Pentax I have previously owned by far.
*The SR is improved over my K5IIs as well
*Colors are more accurate at high ISO levels
*WB is excellent
*More keepers by a wide margin.
Otherwise, the K5IIs was superb and I can hardly tell the difference except for those improvements I listed.
This is from a very limited viewpoint....if I shot in FF mode or for more professional use, I am certain there would be many more K1 advantages. For most APS-C shooters I can't see any real advantage other than those I listed.
For me, I bought the K1 because my K5IIs was badly damaged in an accident near the time the K1 was introduced...so it made sense to try the "FF advantage".
Was it worth the price? Absolutely! That fast AF has ended years of frustration in focusing in low light or crowded outdoor brushy scenes. The K1 focuses in near total darkness and can target a subject in thick brush instantly. My shooting time has increased by two hours a day in early and late low light shooting. Frustrations are gone and joy in shooting has greatly increased.
That's how it is for me....keeping in mind my limited needs and skills.
Considering the price of the K5 at introduction several years ago...allowing for inflation and the much advanced technology....seems the K1 is actually less than what I paid for my K5 back then.....so the K1 is not some out of reach high priced upgrade, it is actually a real bargain!
Regards!