I think there’s a lot going on with this topic. I tried a size down and the exact, recommended size for my braided solo loop. Now that it’s summer, I’m extremely glad I went with the exact, recommended size. Your wrist changes size some through the day constantly. It will feel loose at times and tighter at times. There’s not really a way around that. You can pick. It will either be slightly tight at times or slightly looser at times. I personally found the HR monitor is less accurate when the watch is super tight. Hence my decision. Honestly, I would probably not be able to wear the size down in hot weather, even after it had stretched some.
TLDR: The exact, recommended size from apple worked best for me. Mine has not stretched very much. My wrist just changed throughout the day, making it feel a little different.