I work in the marketing analytics and attribution space and can confidently speak to this topic. While Social isn't the BEST performer, it doesn't carry with it the dire statement of a "complete lack of results" as you state.
With dependencies on vertical and how the advertising is used in known conjunction with other channels, Social definitely does have an assister effect on those other channels. The problem you may be encountering is relying solely on outdated analysis methods which do not appropriately track credit for known users across the entirety of their path to purchase or you're simply just looking at in effective ad buying behavior resulting in poor ROAS.
Done right, Social is definitely valuable for relatively low cost when compared to the much larger channels (based on investment) and can absolutely jack up your return on those other channels as an assister but definitely is not going to be a 1:1 return as the only advertising channel you should leverage if you are hoping for conversion.