Hm
* substantially in the minority for formal use where clarity and an impression of correctness are important
-Formal use is an aberration - language is not formal, clarity is not needed, and the impression of correctness is for lawyers.
* in competition with alternative colloquial terms for the same linguistic niche
-As are many other words and terms. Overlapping meanings is a wealth. People go out of their way to say things in different ways.
* redundant with established terms for the same linguistic niche
-A claim of redundancy requires your assertion that you know language to be a deterministic one-to-one cypher for meaning.
* recognized -- by many of those who use it from time to time -- as a mistake when it is pointed out.
So you admit that people use it from time to time? People tend to back away from corrections of language, both in giving and receiving. If people admit it's a mistake that's interesting, especially since there is no authority that can rightfully claim to decide that it is.
* unsupported by definitions by recognized authoritative references
-You were the one who introduced me to the Vacant Lot Scam. There are no authorities. Language norms are a vacant lot - any linguist worth a damn is descriptive, not normative. The point is not to say "this is wrong", but to say "these people do this, like this".
"There's no such word as "ain't"!" - "My ass there ain't!"
But returning to the windmills; it is in fact relevant to consider what is worth fighting.
You have limited resources. You fight this one, which you can't beat, and it means letting a couple of other petering embers turn into raging brushfires.
