I've received similar DMs from a multitude of people, asking me why Runesmithing was compatible with (insert player group here's) magic or CA, and my answer to such is quite simple.
I don't feel that it should be my job to police who exactly gets access to a neat crafting magic. The point of it is exploration of themes and storylines, and provided that the roleplay is sound, I don't see any reason to outright bar most people from using it - that was never its intended purpose, when I was writing it. I feel like allowing anyone, Heralds or Paladins, Spooks or Holies, etc. to explore what this magic has to offer, provided they've the slots and meet the prerequisites, is the most beneficial to the health of the magic as a whole, and furthermore its longevity. Minmaxing could happen, sure - but that'll happen with anything. No sense in limiting the potential scope of the lore just because I'm afraid that (Insert Player Here) will use it to make their CRP beast character even more of one.