I think Wen will perform well for most younger, healthy, thick haired beauties -- like the models. They could probably wash their hair with mud and be okay.
Those with health challenges -- aging, hormonal, medications, severe stress loads, thyroid issues, etc., would likely be the one's who would have the most issues with a shampoo lacking a good cleansing agent. Maybe issues with some of the 'natural' ingredients, as well. Their hair follicles are already challenged.
I know, since I've been dealing with several of the above issues, leading to hair thinning. I used a sulfate free, creamy product (not Wen) and I had almost immediate increased hair loss,with oily, itchy scalp. I thought it was coincidental, so kept it up longer than I should.
I finally used a good cleansing shampoo and recovery began. I suppose one could use these shampoos without cleansing agents if they used a clarifying shampoo, at intervals, to cleanse and refresh hair follicles. In fact many recommend this, regardless of hair products chosen. We get a lot of buildup on our scalp.
I know now, I do best with a quality cleansing shampoo and light conditioner. Air dry.