You can say “While WUSTL has been a good experience, it has become clear that it’s not a fit for me due to the overly competitive environment…” or whatever. It’s okay to mention “I have had good experiences at WUSTL, however, in hindsight, I might have fit in better in at a college with more school sprit…” or similar. But the essay needs to focus on why you need to be at the school you’re are applying to.
Especially as you are strong student, find compelling reasons for “why this school?” Your grades at a rigorous college will get your app a strong look.