Hmmmm. Would be fair and reasonable to say that all insulating layers, be they wool or synthetic, lose some of their insulation properties when wet? It must also be worth considering the physical state of the person wearing the clothing as well. If you are tired and hungry, even the most efficient insulator may not feel up to the task of keeping you warm; conversely, if you feel rested and well-fed, the thinnest of garments can do the job.
I think that, while it might be interesting to some to scrutinise laboratory derived statistics, for anyone who uses clothing as a means of protection from the cold, the realities of life in the woods or on the mountain can differ from the lab. quite noticeably. The reassurance of the graph and stat. covered shiny label is something of a hollow promise, particularly when manufacturers seem so vague about which fabrics are being used as a comparison. It is a persuasive marketing tool and may represent some imperfect research into the qualities of that fabric; but notice that it is the fabric being tested, not necessarily the garment. Stitch it, seal its seams, put on zips and storm flaps, combine it with other allied fabrics and the nature of the beast changes.
Equally, over time and through abrasion, sweat, wash cycles and the gamut of use and abuse, the fabric of the clothing will lose some of its 'off-the-peg' qualities, leading to a depleted performance, if you like.
Personally, I'm not interested in the numbers associated with insulating properties of vapour transmission rates. If I put on a garment and it makes me feel warm, that's good enough. If it happens to be light, comfortable and seems to complement what I am wearing, then it will be included in my pack.
Naturals? Synthetics? You pays your money and makes your choice. They both seem to work and pretty well, given what we expect of them.