
RNG is just weird. I got most of my Kutas from just randomly harvesting that one random runestone that was on my path, but when I am actually hunting for runes... Nothing. I started accepting that and will avoid runestones when I'm purposely harvesting stuff (or at least not prioritize them over the resource I want at that moment).
To me, the drop rate of kutas is regular and fairly good, but, it is true that it seems to be cycling.
I always have two phases alternating all the time:
1) quality and amount of stones increasing.
2) Suddenly, bad dropping: just one Ta and another low level one. This lasts this way for a while, with Ta + just one else, and then suddenly I get more, and am back to 1).
I farm runestones on a daily basis and always see that cycling happening twice per day at least.
I got 5 Kutas from trove scamps the other night... I didn't even know they dropped Kutas !@#