I’ve been doing just this, and farming runics instead of crafting them!
Souls aren’t a problem for me right now, as I use a dragon soul + hero + 2x necromancy trait team when farming traitstones.
But maybe I’ll regret spending souls to craft minors, when I start powering kingdoms up to 6? Now most kingdoms are power 2, and I usually power up an individual kingdom directly from 2 to 5 all at once. 6 seems a long way off, but I guess it will come well before Pharos Ra since I play a lot.