And their baseline for what Jesus actually looked like is...?
The biblical description of the wounds JC received. The scourge marks, thorny crown blood spots (not typical of an ordinary crucifixion), unbroken legs (also atypical), nail holes, wound in side.
Other than that he must have had a very ordinary appearance for people of that time and place, Otherwise Judas wouldn't have needed to betray him with a kiss, he coulda just said "Go get the really tall guy with the big nose, blond hair, small ears, and a limp."
In other words, the shroud shows an image of a corpse that matches what little the Bible describes about his physical appearance. (If we were supposed to worship his image he would be described in vivid detail)...