I could buy that explanation for the flatter stones, but not for the larger stones. And I come back to the fact that the henge and ditches look extremely quoit-like:
I suppose you don't believe in the devil either then.
The stone in the foreground is an original stone, whereas the others are replacements. We can not know what shape the other original stones had. You can't use replacements as evidence. We only have two clues as to the shapes of the missing stones: the stone holes and their name, "The Devil's Quoits."