Well, you said this:
And my reply was hinting that is doesn't matter if it's a terrible replica gun. It still looks like a gun and could be used in a robbery/threatening manner, hence why it is classed as a firearm.
And I like the way you simply dismiss it as "just give them cash or item and let the cops deal with it." That's too late chum. Ever heard of post traumatic stress? Ask anyone who's been held at gunpoint, then later found it was a replica and ask them if it in any way diminishes the emotions/stress they felt at the time. Guess what the answer is?
There is a very real and good reason that MP-5 is classed as a replica firearm in NSW and I believe that should continue to be the case.