I don’t get your point about myriad.
It is in a similar situation. To quote AHD:
Usage Note: Throughout most of its history in English myriad was used as a noun, as in a myriad of reasons. In the 1800s, it began to be used in poetry as an adjective, as in myriad dreams. Both usages in English are acceptable, as in Samuel Taylor Coleridge’s ”Myriad myriads of lives.” This poetic, adjectival use became so well entrenched generally that many people came to consider it as the only correct use. In fact, however, both uses are acceptable today.
(Note that I use itals for quoting people in the thread and the quote box for quotes from elsewhere; my humble feeling is that this is better than what seems to have become normalized, which is using the quote box for everything and including the entire previous comment in the quote box, rather than just the bit one is responding to, which leads to confusion, at least for me.)