I think you may be placing a bit too much of an emphasis on the PS. It's important, yes, but for most people it's probably not going to make or break your application. You can have an incredible PS, but if your EC's suck or don't really support what you're saying in the PS.... not good.
EC's matter because schools value candidates who have done more than just get good grades and do well on the MCAT. They want people who have dedicated numerous hours to service, research, etc. They want to see that you were genuinely interested in the things that you've done, so you should be able to talk about why you pursued each activity, what you learned, and what it meant to you. For many people, EC's will make you stand out from the crowd, making you more memorable and desirable to schools.
Again, a strong application will have a solid PS and good EC's. Ideally, they work together to show why you're interested in and pursuing medicine (+ a few fun activities that you do for yourself). How you talk about your activities is important: two applicants can engage in the same activity, but if one applicant is passionate about the activity and another does it simply to check a box and can't really talk about it... you can imagine how the first applicant will stand out in a more positive way.
