Who says music and theater majors are easy? Sure, you probably won't cover the absolute configuration of chiral compounds if your life depended on it, but can you act (well)? Can you play an instrument (well)? If you think about it..it's HARDER to major in something completely opposite while doing prepharm/premed/predental/preopt. On top of satisfying your major requirements (hours of practice, memorizing lines, yadayadayada) you have to squeeze in the pre health reqs, whereas if you just majored in chemistry, almost all the reqs are already covered. 🙄
Professional schools also like to see that you major in something you're passionate about, be it aerospace engineering or theater arts. You don't have to like chemistry to like pharmacy, in which case doing chemistry just for the heck of it doesn't guarantee you'll be good at pharm 🙄