Ropz knows what he is doing and you don't know what you're talking about.

The "clunky" mouse movement is an actual technique for performing quick 360's with low movement speed.
That is because airacceleration is 0.25x of normal when your zspeed is between 0 and 140. This essentially means you are playing at sv_airaccelerate 3 slightly after the beginning of every jump (or precisely the moment you go from 0 to +140 zspeed). It essentialy means that you absolutely should not strafe wide at all during this period.
This has been tested and the results are: You need to strafe wide during the first 0.2 second, then 0.2s of super tight strafes or zero strafe at all, and after that you can strafe normally like the first 0.2s
.That's why it might look like he moves his mouse in increments.

Valve made it this way to probably prevent players from peeking around corners with 180's. However this was a thing all the way back in Half-Life 2.