If reasonable means without the spaceships, Uber-people and healing energy crystals then i agree, in theory.
Although the real place might hardly be recognizable as the myth version.
If you know about the small jungle village which, most likely, inspired El Dorado myth, you know what i am talking about.
Yes, without the spaceships, Uber-people, and healing energy crystals. Mostly.
But I think we also risk making a mistake by underestimating the technological gains that might have been made -- or just barely missed -- by those civilizations. I suspect that there were some discoveries made thousands of years ago that either were lost, or barely missed some essential connection with another discovery that might have meant a technological or industrial revolution far earlier than ours.
I would submit that the things lost in the various burnings of the library at Alexandria would have amazed us were we to find them hidden today. I would bet that we would be very surprised at what they knew or what things might have been known if only they'd put a few different ideas together.
It's tantalizing, but of course, imponderable.