If you progress through the chapters this issue solves itself because your income rises much faster than the cost possibly can.
E.G.
The cost goes up 500 per purchase which is a lot at first, but eventually your Mainhall holds 100,000,000 coins.
With a KP cost reset you could trade a coin rain for ~650 KP.
I've been buying KP every day for years and the next one only costs 5% of my capacity.
Measuring the cost of KP by the capacity of your MH seems a bit strange to me. After all, if my MH holds a billion coins but I only have 20,, I only have 20. What you may have meant was that the capacity of the MH implies you are going to generate more coins -- and in general that is certainly true, but it's a correlation, not a cause sort of thing. If you visit, of course, there is a connection, but that's an "extra" thing you have to do to get the benefit of a larger MH.
Thus, to me, it's not the MH capacity, but the ability to generate sufficient coins to meet the quest requirement when the quest requirement comes around. Since there is no guarantee that you will be able to do that, increasing the cost without an reset, AND requiring a person purchase KP (doesn't really matter what you use as they all go up and never come down...), seems a way to bleed a person to death. I pay 428,000 coins for each KP, extremely cheap in comparison to others in CH 17. So every quest I do that requires me to purchase KP, I save 2-3 million coins per each KP over some other players. To me that, by itself, outweighs any benefit in buying KP all the time. But, as we know, that's just a personal preference, even if it makes some sense.
In the long run your observation is probably valid overall, but just based on the wrong or at least a less precise measure of why you can afford the cost of KP to constantly rise as you play.
I'm in chapter 18. My MH holds 120 million coin. A KP cost me 3677k and I probably buy a half dozen most days. Currently, that cost per KP is 3% of the MH which lets me get 32 KP from a full MH. If it were to reset to the initial 500 and go up 500 with each purchase, I'd be able to get 692 KP from my full MH. Then wait until a reset as my MH refills and do it again. No more waiting for KP for a tech. I'd be able to upgrade high leveled Wonders every day or two. Upgrade a new Wonder a couple of times in a day. Sign me up!
Interesting. In chapter 17 my MH holds only 54 million. It's at it's highest level and needs more research. A KP costs me 428k so I can only purchase 126KP with a full MH. If I paid what you pay for KP I'd be able to buy 14.6 KP with a full MH....and since some quests require more than 14, (if I remember correctly), those quests would wipe out my coins.
Maybe there are cases where daily purchase of KP can get you into trouble?
AJ
AJ