I think the perspective depends on the community/ hair type you are 'hanging about with'. Plenty of straight and slightly wavy long hairs CO-wash exclusively and stretch washes far more than they ever did with shampooing, partly because their scalp is pumping out less sebum now it's not being stripped and irritated, and partly because their hair is less dry, damaged or tangled. Many curly girls wash more often, but not necessarily because the scalp itself has become unclean, but because of product accumulation or because hair looks a mess/ can't brush it out.
The right CO-wash product can get most hairs/ scalps as clean as shampoo from sebum or heavy oilings, I use Inecto which is fairly light, actually lathers slightly and literally leaves my hair 'squeaky' - I've CO-washed heavy coconut treatments and another time unbelievably greasy rats tails from not washing for over a week when sick. I've worn my hair straight afterwards and received compliments about how glossy and healthy my hair looked, which I would not get if it looked greasy, dull or full of dandruff.
I don't use CO-wash to add moisture I like a clean fresh feeling, I do it to avoid stripping my skin (atopic eczema/ contact dermatitis) and to avoid my porous hair poufing from the pH/ polarity of shampoo. So it may be different using a 'proper' cleansing conditioner with added oils, glycerin or water soluble cones, I have no experience of that. It might also be different if you have a tendency to scalp problems, definitely seborrhoeic dermatitis should be cleansed regularly.
Remember you can remove even heavy stage make up better with a good cleansing oil or cleansing lotion than you can with most foaming face washes, both oils and lotions can rinse everything clean with water due to the added emulsifiers, exactly the same as the emulsifiers in CO-wash products.