Hard evidence? No, but better garments properly maintained very much do outlast their lower quality counterparts. The issue is very few consumers can assess fabric quality, patterning/construction or fabrication much less know how to maintain or mend items. A well made garment will outlast a poorly made one and a well cared for item will outlast one that isn’t cared for. I do think quality has gone down quite a bit because the average person doesn’t know these things and the market rewards corporations for poorly made goods.