You’re overthinking the “duh” factor. The school isn’t looking for you to explain that cultures are different; they want to see how your personal experiences have shaped skills and perspectives you’ll use as a med student and future physician. The value is not in describing differences, but in showing how living and working in multiple cultural contexts has made you academically adaptable, observant, and effective in communication (consider these exact concepts)
You already have great material: moving between two education systems taught you flexibility in how you learn and work with others; leading MSA sermons trained you to tailor your message to different audiences; and shadowing abroad taught you to interpret actions within their cultural context before making judgments. Those are proof that you can navigate differences thoughtfully and apply that skill in both team and patient care settings.
Your throughline has many different experiences, you don't need to mention them all in great depth; rather, you can mention them in a [place] with [audience/"who else is there] for [purpose]. The important detail is what did you do there and what will you bring with you - academic adaptability, observance, and effective communication. These are the simple topics that ADCOMs want to see and are scoring you on. Your presentation involves diversity but it's a means to an end, not the end in itself.
Don't lose focus on the core piece of the prompt - what are *you* going to do from your experiences