I would say Beacon relied most on it's students for security, but yeah, it's pretty damn easy. It is shown to actually have security guards, but the defense is so minimal it's laughable, and who maintains the servers? Are there even surveillance cameras? Since Ruby ran into Cinder, she would not have had any kind of freedom to disable surveillance, so she would have been spotted, and sharper minds would suspect her whilst she blends in among the students. Would have been neat if she had some kind of stealth Semblance, since her fire seems to be from obtaining a portion of the Fall Maiden's powers. If they showed her stealth semblance, but also her fire abilities alongside it, it would confuse the viewer until it's explained with the Fall Maiden, it would have been something fans could speculate about, while allowing her to stealth around as she pleased.
And I don't think she hacked that, she planted a bug, they're usually stealthier, and are a setup for things to come. Then again she should definitely have been spotted and the systems checked after that, so... I dunno. I guess they just wanted Ruby to have that encounter and they needed a fight sequence?
As for womanly women, there are some pretty big gruff men as well among the students, especially third years, or even a mature woman in Coco, so I think that can be overlooked.
To be fair it was Emerald's semblance that rigged the way the match was seen, but you would think that some of the students and teachers would know something is wrong.
By the way I would say we make our own original story instead of just an AU. I don't think we have to have all the characters from the original show if any, or even passing mentions if we need to, but we should focus on whatever threatens Vault instead.