Not necessarily the case. I have successfully shot plenty of Provia (in 4x5 no less!) at mid day with nothing more than Sunny-16.
The only variable is in our abilities to recognise it.
Whilst we might not be able to accurately measure actual light levels using our eyes due to the fact that our irises open and close to compensate, we can recognise contrast which is also dependant upon the diffusion added by clouds.
for my own work at least it might be sunny 11, but a lot of the time it is sunny 8 or 5.6 ( box camera ) ...
I do a night photography project every year and have found that similar rules apply at night. The moon is usually as bright as a sunny 16 day (If you were to take a picture of the moon), you can zone meter accordingly and get results that work. This comes in handy as sometimes batteries freeze in Canadian winter nights making light meters moot.
I shoot a lot of transparency film, and don't have or use a meter.
Apologies for the image quality and 35mm... I don't have a scanner. But just as an example this scene is not so straightforward as mid-day sun on your front lawn. Once you've got an eye for it you can figure it out, most of the time you just need to consider the deepness and contrast of shadows for a good indication of how bright it is. A meter becomes more handy the duller it gets, when you can no longer rely on shadows to give a good indication of the light.
I would not however advise anybody to not have a meter with them. When you need it, you'll really need it. But your eyes can be pretty darn accurate for most situations.
I have a metered prism for my ETRSi and a couple of ancient handheld meters which came as part of ebay camera lots. I don't tend to use them though as I like the waist level finder (and I'm not so keen on the bulk of the speed winder if walking around with the camera, without that I find it very hard to hold the camera steady with a prism finder on). I only shoot B&W negative film at the moment and for that I find Sunny 16 works pretty well.
Of late I've taken to trying to guess the correct exposure with my 35mm cameras before I activate the metering. I'm usually right to within half a stop or so, and it makes a good check for metering faults (like the ME Super I had which underexposed by two stops until I dripped lighter fluid into the film speed mechanism and worked thirty years of gunk out).
What I have noticed is that it's better to look for shadows than it is to try to guess light levels, especially if you have self-tinting glasses or sunglasses on. You also need to think about location - I'd guess that my shaded front garden would probably be about f5.6 at the moment, while the sunlit part of the back garden would be f11-f16.
I haven't been claiming sunny-16 doesn't work, at mid-day and in other simple lighting conditions. I am claiming it's no substitute for a meter. The reason being, that if you are filling the whole scale of whichever film you are using there is no exposure latitude; any deviation and either the highlights or shadows are not what I want. I like to know what I have on the film before I process it (aka previsualisation), and my printing is done with an enlarger - no fauxtoshoppe - or contacts from 8x10.