This article claims the idiom predates Merriam-Webster.

https://grammarphobia.com/blog/2020/12/one-of-the-only.html

I'm likewise aware that using literally to mean figuratively isn't particularly new, but the phrase's existence or age isn't the issue.

I respect your commitment to influence the evolution of the language :)

Heh, I just write too much too readily about unimportant opinions, and a lot of people read sentences longer than a few words as incontrovertible proof of being triggered :D

Also it's difficult not to call out the hypocrisy of descriptivists simultaneously saying that basically anything goes, but my preferred use of language in particular is wrong and I need to listen to what they prescribe :P

Words change. Meanings change. This has always happened an always will. If enough people are ironically using literally, even if unknowingly, then yeah, the meaning will change and we need things like dictionaries to describe this new meaning.

You're not wrong, but IIRC "only" has meant "one-like" since old english.