Good point, wrong example...
Total Coalition deaths in Afghanistan since 2001 : 2583
Total Taliban deaths in Afghanistan in 2010 : 5225
Total Taliban deaths in Afghanistan in 2009 : 4610
Total Taliban deaths in Afghanistan in 2008 : 3800 - 5000
etc etc
Source Wikipedia
Now if you start to include civilian deaths it changes a bit, but you still can't say that the Taliban is causing "mayhem at relatively low cost to a much bigger force of heavily armed soldiers. " unless you have a very broad definition of "low cost".
Based on the number of fatalities from both sides I would say they're pesky or maybe irritating, but I agree with your point, if not the example you used.