Engineering is less pertinent to the practice of pharmacy. A 3.7 in biochemistry is more appealing to a pharmacy school admissions committee than a 3.4 in engineering. Calc 1&2 are the highest mathematics courses that pre-pharm takes for a reason. Even if you got a 3.7 in mechanical engineering and a 3.4 in biochemistry, admissions still isn't looking for a human calculator, and neither are employers. Can everyone do engineering, no it takes a certain type of mind. Can all engineers be good as a practicing pharmacist? No. Medicine, is a different story, if you want to do something that you might feel better appreciated as an engineer, I would look into medicine. They love people who are innovative, have that deconstruct reconstruct mentality. "hardest" is determined by what you're least interested in/least successful in. For ex., getting a bachelors in English would've been impossible for me because it's boring and I probably suck at most aspects of language arts. Or getting a BFA in dance would be hard, because...I don't dance much/at all.