Oh I see, so MBBS is just a shortcut version to becoming a doctor, as opposed to postgraduate medicine, but it requires a significantly higher ATAR score and UMAT score.
It's not a shortcut version, it's just a different model.
E.g. LLB vs. JD - they're two different pathways to get to become a lawyer.
Traditionally British medical schools followed the undergraduate (MBBS) pathway whereas US medical schools followed the graduate (bachelors + MD) pathway. Up until recently, Aus. followed the British in that we only had MBBS - but UoM (and other universities) have, since, introduced graduate entry pathways.
In order to get into graduate medicine, you will need a high GPA, high GAMSAT and a strong interview. It's no easier to get into graduate medicine.
A biomedicine degree MIGHT lead to an MD, there are many who do biomedicine for other purposes - e.g. dentistry, physiotherapy, biomed engineering, research, teaching...etc.