GP's use is listed here https://en.wikipedia.org/wiki/Exception_that_proves_the_rule... under "Proving the validity of a rule of thumb"
I don't dispute that people use it that way but it's objectively a misuse. The phrase's misuse implies that evidence against a statement supports the statement.
> In many uses of the phrase, however, the existence of an exception is taken to more definitively 'prove' a rule to which the exception does not fit.
> In what Fowler describes as the "most objectionable" variation of the phrase,[1] this sort of use comes closest to meaning "there is an exception to every rule", or even that the presence of an exception makes a rule more true; these uses Fowler attributes to misunderstanding.
Try to understand that there is no individual ownership over turns of phrase, and that they tend to shift around over time. Bugs Bunny turned Nimrod from a byword for a competent hunter into an insult.
This is natural and all of your favorite words have or will be subject to it as long as there are humans to communicate with them.
Btw, let me add my personal pet peeve: "egregiously" somehow went from meaning "very good" to mean "very bad" in American English.
In my native language "egregiamente" still has the original meaning so I was confused for a long time.
The original meaning of 'prove' was more like 'test'. The original sense was therefore opposite to this.