Yes, it's not workable imo, either 1/ the group is small enough that LEA goes after and harrasses all individuals or 2/ large enough that nobody can place trust in it because nobody knows(of) all the members.

Ring sigs usually have exculpability, meaning you can't be proven as the signer even if your key is coerced out of you. But similar to OTR, it sounds nice on paper, but (maybe?) doesn't help too much in practice if LEAs are harassing and intimidating you.