The issue is that there are about 180 posts tagged as runes just because of Nanashi Mumeis rune-shaped hairclip, and I would certainly not call it "text".
I also agree that most of the time runes are used merely as a stylistic choice rather than actual text, and tagging what is essentially just random gibberish as "text" is quite the stretch, and even if we split the tag into just runes and runic text, I doubt many people would be able to tell the difference, so chances are that runic text would end up probably just as a undertagged tag with a lot of mistags.