Is their any reason to apply if you are not accepted to the USMA SLE? I had above USMA average grades and stellar leadership in numerous clubs. Is it best to continue or are chances slim?
Take it from someone who just went through the process - SLE does not matter in the overall application. In fact, I don't even know if it goes on your application at all during your actual processing.
Last year (when I applied for SLE), they limited the sessions from 2 down to 1 due to the budget cuts. That means very few people went. I was not one of them, but I received an appointment in the end.
I am friends with a grad who used to be on the board of admissions up there, and he said SLE is really more competitive than USMA applications because it is a lot of the ivy league applicants with amazing test scores that are looking to boost their resumes by adding that to it. Sometimes, the board is even looking for different things during SLE selection, so people with amazing files are not selected for whatever reason.
On top of this, a TON of my accomplishments came after the application during my junior and senior years. I didn't have a strong ACT on file, and I really gained a lot of leadership positions in my school and community AFTER I was denied. So there is really nothing you should take away from that. You need to focus now on making your file stronger for the application.
And, +1 to Jcc123 too! USMA uses SLE as a recruiting tool. I was told that some people who were closer to USMA than others were not selected because admissions is trying to reach out to people further away (this came from someone who worked with USMA). If candidates know a lot about USMA, and maybe they don't have a stellar application for it, they will offer a spot to someone who maybe doesn't know as much. It is truly meant to recruit a larger number of strong applicants.
To make a long post longer: read the threads on here, and keep moving forward.