You're right Mr.H
The sexy Wessex monuments overshadow a few mingy cupmarks. but I reckon we know different don't we? Cupmarks are personal, they represent our ancestors putting their hands upon the rocks, not the collective, the individual.
The intervening centuries dissolve when you're next to a nice bit of rock art. Complexity is not essential. If anything, I reckon the more complex the motif, the more removed the modern viewer is from the moments of the motifs' creation.