Welcome to MSO.
You’ve listed a bunch of clear reasons why UWA objectively appears a far better choice for you.
A uni being the most prestigious is really not going to be of much value to you as a medical student, and should not factor into your decision making. A higher “academic standard” should also not be a factor (it’s also not true - there is no clear way in which to compare this between different universities, however it may be defined).
What matters is that you graduate with a degree which qualifies you to be a safe and competent intern, which a medical degree at any Australian university will allow for. To me it seems a huge bonus that you have the opportunity to do this in your home town, with the support of your family, friends and girlfriend, while being able to save on accommodation, and ultimately with less of a HECS debt than 7 years of study will result in.
Could you clarify which specific opportunities you are concerned you won’t have at UWA that might be offered in Melbourne?