if you're not being facetious,

in English vernacular being a frustrated X (as in a frustrated academic, frustrated poet, etc.) means that the person is actually not that, but have in some way been prevented from being the thing (frustrated) and have perhaps rancor in regards to the frustration and towards those who actually are the thing (this second feature being sometimes implied depending on who is doing the description of the person as frustrated)

on edit: formatting, clarification

Thanks, I wasn't aware of the 2nd meaning. I also interpreted the "frustrated academic" as "an annoyed academic", rather than "an unsuccesfull academic".

I'm thinking maybe it is no longer as common an expression as I thought, given the people who've mistaken it here.

I think it didn't help that they used both meanings of the word "frustrated" in the same sentence. By adding "perhaps my frustration is unwarranted", it puts emphasis on the fact they are frustrated, not that they failed to become an academic. It leads the reader to believe they are in fact still an active academic.

I was only dimly aware of the second meaning of the word so I'm not sure how you would interpret it if you had a good understanding of the multiple interpretations.

As an English speaker, my only interpretation was that you were an academic frustrated about academia.

https://www.ldoceonline.com/dictionary/a-frustrated-artist-a... - came up if I search for 'meaning of frustrated poet' which is the kind of thing where the phrasing most often comes up.

That isn't even the same user.

He is proving his point by contradicting himself, a true mathematician.