Hi matt_llvw,
Originally the kanji used the meaning “strange” while the vocab 妙 used “odd.” We wanted to find a word that fit both of them, to make it easier on the learner, and went with “peculiar.” We also felt “peculiar” would more precise for the nuance of this kanji. Compared to “peculiar,” the word “strange” has more of a negative connotation, at least to me. But 妙 feels more neutral and appears in a number of positive words like 巧妙 (50) or 妙案 (not in WaniKani yet but planned as an addition!).
Sometimes we do end up splitting hairs like this to avoid overlap with similar kanji or vocab — in this case with 奇, which has the visible meanings “odd” and “strange,” and 変. I know it can be destabilizing as you say and I apologize for that. For the 妙 kanji we do still keep “strange” and “odd” on the allow list, to avoid that disruption as much as possible.