Mel Gibson has absolutely no frakkin clue about the Mayan culture. In his interview with MTV Movie News he goes on to say that his portrayal of their civilization is fairly accurate.
The Mayan civilization lasted powerfully for roughly 2000 years. From 500BCE to 1500CE. The Mayans were writers, sculptors, astronomers, and mathematicians. Their calendar is accurate to this day.
Their writing system is one of five independent writing systems that humans have ever used. All other languages and written text are derivatives of others. The Mayan hieroglyphic writing is the most complex phonetic script in the world.
Eight million Maya still live in North and Central America. They are not lost. They are not timeless. The Spanish church did not succeed in destroying them or their culture.
Gibson inaccurately depicts the Mayan civilization. In the movie their cities date to the 9th century. However, the Spanish arrived in Central America in the 16 century. He even uses Mayan images dating back to 300BCE.
The Maya were not organized into small bands of gatherers and hunters. The Mayan organized into complex farming villages. Their society was made up of farmers, masons, warriors, scribes, priests, artists, musicians, noble elites, and holy lords. They were complex societies that Gibson cannot possibly grasp.
The movie echoes the time of the Classic Mayan collapse, 9th and 10th century. However, the Mayan at this time were not diseased and dying. It is more likely that they were far better off than their European counterparts.