Priority, it would be difficult to speculate as to how many students from Science 'get in' to medicine using that logic...not all students doing Science will want to apply to or get into medicine - since it is a much broader degree it will attract a cohort with collectively broader interests. I guess it is easier to look at the 'success' rate from Biomed --> Medicine since most students doing Biomed will want to do Medicine...but not all will, again, because some will want to do other professional health degrees like Dent/Physio/Optom and some other things entirely.
I chose to do Science because I wanted more flexibility in my major/subject choices (potentially, at that time, a major not related to biological Sciences) and I wanted flexibility to go where I wanted to go on exchange when I wanted to go on exchange...but of course spent like months on end deliberating about whether to accept my Biomedicine offer before coming to the conclusion Science was a better option for me.