Fair point, but OP may find the course material and unit breakdowns at Monash to be better (the main reason I turned down my offer to UoM biomed in favour of Monash's).
I don't really believe you can compare course material until you've been to both universities, and when you are referring to unit breakdowns, I'm assuming you mean the Monash handbook / UoM handbook. I personally believe that neither should be a factor when considering which uni to go to. Just because one subject may be more detailed in a handbook doesn't mean that it is a better class.
They've also stated they would like to do medical research combined with clinical practice - Monash certainly teaches the research skills and the clinical practice could follow though it is hard to argue against a guaranteed MD place at Melbourne unless one genuinely didn't like it there.
I haven't done Monash's course (obviously), but I feel that if you're doing a BBiomed anywhere, whether that is RMIT, La Trobe, or either of the two research-intensive universities being Monash and UoM, you're going to learn research methods through your classes. Clinical practise doesn't influence the decision because it is not going to be found in an undergrad pathway.
You're suggesting about Monash BBiomed is a good one, especially after the new pathway to MD. But there is no way you would / should turn down a Chancellor's for anything but a MBBS.
EDIT: Not meaning to sound rude btw, just providing an rebuttal to your post!
To the OP: For me it breaks down this way:
If you want to do your Med degree by itself, quickly, then go to Monash.
If you want to do your Med degree with an Arts component, then it is sort of a moot point IMO, because you'll be adding time onto your degree (or overloading, someone correct me I couldn't find the details) if you do it as a diploma at Monash, and you'll have to take the 3 + 4 year pathway at UoM taking arts subjects as breadth. If you also take on the BMedSci at Monash, you're looking at a one year difference between UoM and Monash, so you're comparing a BMedSci at Monash vs a BBiomed at Melbourne.
If you want to explore other fields during your undergrad, UoM.