Yes, I agree that the stones may have been brought (or taken) from Wales over a long period of time (longer perhaps if they were brought than if they were taken).

I think the important point that you put your finger on is that it's dangerous to assume that the ancients (apologies if that word grates with anyone but it's a convenient one) functioned within the same sort of timeframes that we in the West (and I emphasize the West) function in today.