That PGP handles armor, escaping, and comments badly, and clients handle display of the signed text badly, do not seem like they mean that the concept of cleartext signatures are inherently flawed.

Really? To me it seems that what’s really harmful is assuming a long string of high entropy hex bytes is a valid signature.

Both detached signatures and cleartext need to be run through verify, so what gives?

Does gpg not error when the post-verification output file doesn’t match the cleartext? That sounds like a bug in gpg