That said, and as others have mentioned, markdown is not as well standardized and it seems like just about every site renders it differently, so there are a lot of edge cases to handle. Lemmy also has several unique implementations of things, such as spoilers, superscript/subscript, and the ability to tag users/communities without a hyperlink.
In fact, one of the things Thunder failed on (table alignment) is a known bug in the markdown library we use. :-)