I don't know where you are getting your information from re the number of enemy casualties, but I don't buy the body count metric. We tried that in Vietnam. If Iran and Syria keep on sending people in, there will still be a level of conflict and insurgency. If we can dry up the water the guerrillas swim in, the insurgency will die. It took the British 12 years in Malaysia. We need patience and perseverance.
I get my data from daily briefings, from reports from the field (friends and former students there), and other sources. I'm confident in them. This equates very well with the rates that we were killing "insurgents" in the Filipino Insurrection.