I contest this notion because the development of doctrine is toward greater clarity. It may be the case that there is a more complex meaning to be considered that resists easy understanding. A movement toward clarity may lead to more and not less to consider. Consider John 1:1: "In the beginning was the Word, and the Word was with God, and the Word was God." What is "Word"? You really only begin to appreciate the meaning in the original Greek, "Logos". And that by itself can be contemplated inexhaustibly.
So this suspicion that it was an exercise in obscurantism is unsubstantiated.[0]
If this is a neologism, then it suggests that no existing Greek word was able to fully articulate the intended meaning. It may have tried to capture a meaning available in Aramaic [1]
[0] Not a fan of Karl Rahner, but I think his characterization of "mystery" as "inexhaustible intelligibility" is much more accurate that the modern implication that mystery is impenetrable obscurity. On the contrary, it is penetrable, but inexhaustible. And that would agree, I think, with the notion of the Beautific Vision.
You have provided your own examples. "Development of doctrine" seems to refer to events in a time necessarily much later than its original composition.
I'm not sure how I provided examples of mystification. Rather, whatever the merits of my particular example, I think I rather argued against the idea that "epiousios" was intended to obscure and to obfuscate rather than to clarify by arguing that this would go against the development of doctrine which tends toward greater clarify, not obscurity. I'm making two points: against mystification by virtue of the development of dotrine and for the idea that the term may have been coined to express something Greek had no word for. Don't confuse the two.
In any case, the lack of examples and explanation to support the claim that mystification is a practice in this context is conspicuous. It smells of prejudice, frankly.
If you are unaware of religions coining official mysteries, let me recommend any introductory course in comparative religion. Sometimes the word even shows up in the name: https://en.wikipedia.org/wiki/Eleusinian_Mysteries
And, if you do not understand how "development of doctrine which tends toward greater clari[t]y" implies a progression of events in time that can, perforce, have no effect on events that preceded them, let me suggest: https://en.wikipedia.org/wiki/Causality
My guess is the word was inserted deliberately to mystify. It wouldn't be the first time.