The real issue here is that it sounds like you have moved into a building that has serious problems with overcrowding. Unlike many others, the Owners Corp is trying to do something about it.
Your beef is with the real estate company who didn’t tell you there was an issue with security. But setting that aside, what do you hope to achieve by challenging the security measures and finding out why security has been eased?
It sounds like you have already won, as far as security being recalibrated goes. What else do you want? All security measures to be removed so that you and your girlfriend can come and go as you please?
You are part of a community and you really should be trying to fit in with its needs rather than trying to make everyone dance to your tune.
The long and the short of it is that you are in the wrong building for what you want from a home. There are others although they may not be as conveniently located or comparatively inexpensive.
Perhaps you should be chasing your real estate agent to let you out of your lease rather than trying to undermine laudable efforts to make the building liveable for everybody.
Trust me, the building would not be paying for additional security unless they needed it. If i were you, I would spend my time looking for a building that was better suited to my needs rather than wasting it pursuing the issue through NCAT which is either going to fail or make life more difficult for other owners in the building.