Not untrue for sure. My experience weighs heavy on sound and rpm in conjunction with temp readings. I key in on exhaust header nuts within seconds of shut down to try to limit testing variations. Running tests with infrared meters seems very erratic. 160 to 220 would be typical of poor test quality in my humble opinion.
Doggy, less than full rpm acceleration and less than normal top end rpm, variation of sound are noticable indications of dropped or dead cylinders. Cylinders not running are usually just a small amount above ambient.
Lot of factors to consider. Fuel mixture and ignition consistency also may play a prominent role. Some of the ignition modules are finicky. Inconsistent at different voltages etc.