There is more evidence in as to what caused the collapse of the Classical Mayan Empire.
Tainter would say that they became to complex and were no longer able to adapt to increased challenges. Diamond would say that they slowly degraded their environment until a modest reversal caused the whole house of cards to collapse.
Both of their theories are loose enough that they can claim that the evidence that a period of extended drought coincided with their collapse. But the problem with such loose theories is that they have little real predictive value. How complex is too complex, and how much degradation is needed?
Bruce Bower, Science News, 8 November 2012 (hat tip: Big Picture)
His team analyzed a stalagmite that grew in Yok Balum Cave from 40 B.C. to 2006 A.D. Rainfall estimates for each year of rock formation were derived from measurements of oxygen that accumulated in the stalagmite as runoff from rains entered the cave.
Yok Balum lies near a half-dozen major Classic Maya sites. The scientists compared the climate data with historical records, carved on stone monuments at these sites, of Maya warfare and political events.
Researchers have argued for decades about whether the Classic Maya collapse stemmed more from droughts or from warfare and weakened political systems. Kennett says the new evidence is consistent with climate changes interacting with social forces to pull Classic Maya civilization in different directions.
Douglas J. Kennett, et al, Science, Vol. 338, November 9, 2012, p. 788
Population increases and the expansion of Classic Maya polities were favored by anomalously high rainfall and increased agricultural productivity between 440 and 660 C.E. High-density Maya populations were increasingly susceptible to the agricultural consequences of climate drying. We propose that a two-stage collapse commenced with the 660 C.E. drying trend. It triggered the balkanization of polities, increased warfare, and abetted overall sociopolitical destabilization. Political disintegration in the Petexbatun region foreshadows two multi-decadal dry intervals that further reduced agricultural yields and caused more widespread political disintegration between 800 and 900 C.E. This was followed by a second stage of more gradual population decline and then punctuated population reductions during the most extreme dry interval in the YOK-I record between 1020 and 1100 C.E.
It seems to my mind that the biggest problem is that people expand to the limit of the calorie supply. It doesn't really matter how advanced, or complex the society is, be it the Homeric Greeks, the Romans, or the when the weather turns against them, they die off. Even hunter gatherers had these problems. They are just not particularly well recorded because most non-agriculturalists did not leave enough permanent remains to make their collapse very clear cut.
What makes the big collapse impressive, is the height from which the fall takes place. In the case o the Maya, all the way from the top of a very tall Pyramid.