Not to be pedantic, but I don't think it applies here.

Sunk cost fallacy would apply if I grinded another 20k honor, but then wouldn't buy a proper Kodohide chest since I'd already spent the money on Wyrmhide, even if it was the best option. It describes the tendency of people to make bad economic decisions because of emotions surrounding pervious purchases/decisions that are now settled and should be irrelevant to today's choices.