Yep so in that battle Rune Crafter shows his #1 use case, which is countering Mycelic Slipspawn. While that's a cool use case given Slipspawn is a highly used card, I don't think it justifies Rune Crafter's cost, because frankly he doesn't have any other use cases in my opinion.
To me it's similar to Suidae Shaman, who pretty much has 1 utility in the game at the moment and that's to hard-counter Inevitable. That's why both he and Rune Crafter are in the C Tier in my opinion.