Counterpoint: I see many threads that get off-topic from the original post, and yet downvotes for them seem…random. Some off-topic sub-threads become lengthy and lively.
Colour me "confused".
Oh well, I suppose I'll start calling everybody a "she" by default, then.
From my understanding and reading, the word's exact meaning seems somewhat ambiguous, but may be estimated from the context of the surrounding verses. So, I think the intent was partially conveyed, but without other primary sources it's difficult to have an absolute degree of precision.
This is why I think the argument you made is the most-likely-to-be-correct argument (contemporary use being influenced by the NT). It's also why I'm not sure there's any debate to be had here, nor why the question to you was raised. The Wikipedia article is quite clear that no other ancient texts from that time period contain the word.
So what do scholars do? The best they can!
I'm an atheist but I know this prayer by heart. I must have heard it hundreds of times. Its sound is deeply ingrained in me, even if its meaning is vague when it comes to that one word (and others... "εισενέγκεις"? wut)
Besides, when I was a kid I thought the prayer is talking about a guy called Amin who's cunning ("ο πονηρός Αμήν"). I just learned the words by heart, I didn't now what they meant.