Hi BHelemet, for what it's worth my response to your questions is maybe trust more in the ingenuity, skill and dedication of a driven community when they put their minds to a task (for whatever reason - homage to the past, money, desire to create a landmark to attract tourists, etc) than some kind of unreasonable assumption regarding such massively out of place and time landmarks actually being there from a bygone age.
I have to agree. While the idea of timeline manipulation is fascinating and what it could mean for our present and future, I tend to think it's more to do with subtle changes rather than overt structures that appear out of place in different geographic regions. Although, I'm not ruling that out either in all cases, just that some credit should be given to the ability of our ancestors.
Mainly, I think it's easier for us today to look back on people 3 or 4 generations before us and assume they had limited basic knowledge. As the saying goes about now, never has there been a time that so many people know so little about so much. I think it's reasonable that people prior to the internet age knew their vocation inside out, back to front, and upside down so to speak. I have no doubt that the examples presented were created by clever people of the time.