So forgetting scientific studies for the moment: if you just walk around in a city, is that apparent to you? Do you think, "Wow, there sure are a lot of different types of people here?"
My answer to your question would be a qualified no.
You'll see more phenotypical diversity walking around New York than Nairobi thanks to globalization.
With that said, the qualification I'd put on that is that if I consciously think about what region of the world I've seen the most variation in body plan/portions and facial geometry, I'd probably pick East Africa. You do do encounter pretty much the full spectrum of shapes human beings come in.
I will also say that I remember being surprised by how much variation in body shape I saw in China. Maybe this is pure western ignorance but I had an idea in my mind about what the average Chinese person looked like and I found myself having to adjust my expectations in ways I have no had to do anywhere else.
The last thought I'd leave you with is that you absolutely should make it a priority to visit East Africa. Kenya in particular is where I always tell people to go but Uganda, Rwanda, Ethiopia are all good options. It far exceeded my expectations.
Stay out of Nigeria though lol