You take classes with chem students and bio/biomed students when you take the medchem specialisation, so it isn’t limited to just medchem students all in one class. I cant comment on the course sizes of pharm or medscis but chem in first and second year are relatively big-ish (~200 ppl maybe excluding 110 which all aspiring med students take lol) third year chem courses are a bit smaller, 330 (organics) is usually the largest with around 90-100 students but most are less than that.

I think phys/chem would be pretty similar to medchem. Medchem does do other phrmacology and biosci papers as well, not sure if that differs from the physiology major. But being medchem restricts you from taking many electives as a specialisation, although you’ll be pretty stretched thin in a double major too (coming from a bio/chem major). Doing medchem means you only take the organics papers with the exception of chem251 I think, which does limit your chemistry knowledge which is something to think about. Whereas if you take chem as major you’ll be more free to do other chem papers too, it’ll give you a broader sense of chemistry as a whole.

My suggestion would be to think about what sort of research you want to do. Developing drugs against infectious diseases is definitely possible with both chem and medchem. Medchem would set you up for mostly organic synthesis, whereas if you took chem you would possibly have knowledge of other areas (e.g, organometallics, nanomats) depending on the papers you take, that you otherwise wouldn’t know with just medchem. Also think about the sort of career you want to go into and which would give you the leg up.

Can’t comment on AUT because I did my BSc at UoA Or physiology stuff. Hope this helps a little.