The word "prove" has largely changed its meaning, it doesn't mean "test" anymore, although a few usages from previous centuries survive, such as military "proving grounds." So yes, it's very interesting that an old phrase that once meant 'a circumstance that challenges or makes one doubt a rule', gave birth to the modern phrase that means pretty much the opposite: "makes one more confident of the rule, in the end, after all." But the latter phrase exists, the former is part of history.
Language changes constantly, and meanings often flip from one century to another. The previous meaning of "prove" doesn't obviate the modern usage inside or outside of the phrase in question or turn the clock back. That particular horse escaped the barn, long, long ago along with tens of thousands of other changes in the last few centuries. "Probable" existed before probability theory did, and it didn't refer to odds or math; it just meant "respectable."
I could follow your own suit, I suppose, and compliment you by calling your comment "smart", since that word used to mean "painful" in olde english and you prefer the old ways. But I won't. (I'll just say your comment was interesting, and not quite the full story.) I roll with the common currency: language as it is. Print greatly slowed these sorts of changes, and the internet will slow them even more, of course, as the decades and centuries roll on.