Here is what people get wrong, They think the sunny 16 rule tells you to shoot at f/16 and all they do is shoot at f/16.
The purpose of the Sunny 16 rule is to tell you an Exposure Value for a given light condition and a way to make it easy to remember.
So therefore Sunny day f/16 ISO100 1/100 NOW you use your photography head to know that Exposure value (EV15) is also f/8 @ 1/400 and f/4 @ 1/1600 and f/11 at 1/200 Etc etc ( all are the same exposure) ( hahah I did that quickly in my head so forgive me if I F'd one up)
It's not about shooting at f/16. It's taking a Known Light value and using it against a Known ISO/ASA rating and giving you one number to go with, from there you can extrapolate every other combination that s the same Exposure value