That's not even what he is talking about dude, he is taking about "3+ mobs" and he is talking about sleep. There are 2 jobs that have access to sleep, and one has holy and the other one has flare. It is literally grade 3 math to take a quick look at potency and see that by using sleep you're denying yourself the ability to use your most powerful skill.
If you use sleep in a 4 man past 50 you will either be laughed at or just have the mobs woken up, and you deserve either.
The really funny thing is that he is a WHM so his only other option is aero and stone 2. He is saying that 170 potency is faster than 200x3+ and completely ignoring that holy is also a CC ability, it stuns. It's like sleep it stops enemies from attacking except it doesn't stop you from attacking. Which is more relevant to what you're talking about because people stunned DKs not slept. The idea that he seriously does this in 4 mans is practically trolling.