That might have been the case fifty years ago, when thick, heavy pancake makeup was the only option. Foundation has come a long, long way since then. There are all kinds of coverage options. Some are very sheer and dewy. Also, application is key. It's possible to cake it on and end up with the effect you describe.
Yes, it's true that our natural skintone varies. God also gave females hair on the legs and armpits, but we don't leave that in its natural state, either. :)
"If someone is appearing under harsh lighting conditions (i.e. on stage or in a studio), foundation makeup is essential to overcome the skin's natural transparency, as overly-bright studio lighting makes a person's natural skin appear pale and bloodless."
True.
"A skilled make-up artist strives to re-create the appearance of natural skin tones, even though the materials are opaque. When done well (and IMO sparingly) the results are uncanny. But under natural lighting conditions, I see no reason to do so, and from this man's POV, the average woman must be using a paint roller to apply their make-up"
Could be. It's too bad...there are countless Youtube videos showing proper makeup application.
With all due respect to you, Alex, you don't see the reason for it, but you're not the woman looking in the mirror. Let us be the judge of that, and we'll let y'all decide the length of your sideburns.
In normal day to day wear, I think that if someone is noticing the makeup, then the application has failed.