an epq doesnt mater. the fact that its art does not matter; med schools see your a levels as a minimum requirement with no weighing (other than exeter afaik, they weigh grades only not subjects). there is no such thing as a "competitive subject" in med applications as long as you have chem+bio.
if you're getting an A* in art keep at it because itll keep you in the safe zone, by reducing the chance of something like an A*A*C (worst case) which can result from replacing art with a subject thats more traditionally "better" but you're worse at
also going to oxford doesnt matter. in 20 years time when youre applying to a consultant job, the hospital isnt going to ask you where you went to med school, and even if they do it doesn't change the fact that youre a doctor on the same level as the oxford graduates. so just apply where (i) you will get in, and (ii) would like to live for 5 years.