No-one will care, just do amazing in your main 3, admissions tests, GCSEs etc. Physics "looks" better because it's a more traditional A level
If you think you won't do very well in it/you dislike it, drop it - it won't get you into medicine. And it's very unlikely that "two students are exactly the same etc." if that's the case, Oxford would pick better interview performance and Cambridge would probably pick better academic profile (namely BMAT).
EDIT: just saw your above post, yep am a medical student in London. Never applied to Oxbridge, but have friends there etc. Very familiar with the system as I volunteer-tutor medical applicants etc. If you want to get into Cambridge, get high 6s in section 1 and 2 of BMAT and you're practically in (plus good UMS at AS would be icing on the cake).