This is what I heard from a student interviewer, so I don't know if this is true or not.
Sometimes they don't always accept the best student simply because sometimes the school is afraid that the very top students would reject them and go to the top tier school. For example, if u score 1500 on ur SAT, did volunteer work in the peace corp, and had some senator write u a recommendation, some state schools would not accept the student simply because they know it would be a waiste of time, those students would be attending an ivy league school, not a state school. Similar thing happens at some pharm school. In order to gurantee a descent size class, they accept the best students from each interview session, and not the best student overall in the entire interview season.
In addtion, ur essay also saids a lot about u. U would have to show them why u want to become a pharmacist (it better not just be about the money and the stability of the job). U have to show them that u want to help society and show them why in this way. U can help society in so many other ways, why as a pharmacist. Also show tell them that u also have thought this thing through by mentioning what the role of the pharmacist is and what is the future of pharmacy. And are u willing to be a leader in this field and in ur community.
Also some pharmacy schools I know try to screen some students who want to go to medical school, but chose pharmacy school as their backup plan. One of the things I know some students get ask is, did u ever apply to medical school. They don't want pharmacy school to be ur second choice. Hope this helps, pm me if u have any more questions.