What direct drive "smoothness" truly means?

When people compare OSW build between themselves this word "smoothness" always pops up. They say that Lenze is best, then Kollmorgen and Mige at the bottom.

No one really gave an explanation why something is smoother and what that means. After making a stepper direct drive and spending a lot of time with it the only thing that I can compare this smoothness to is cogging on my stepper.

Does this word implies that Mige has some cogging and torque unevenness like a stepper, but much more subtle or is it just that Granite hardware was behaving differently between multiple motors and people were liking force feedback output from Lenze and Kollmorgen more than Mige?

I'm planning on buying a servo like mige. However money doesn't grow on trees and hoverboard motor turned into a servo would essentially be the same thing just with an outrunner motor, like fanatec DD1 and DD2. Cost of hoverboard motor is around 30e, encoder can be found between 10e and 20e, some pulleys and manual drilling and there's a wheel for around 50e. Small versions of mige motors with around 10 Nm cost 250e at my local reseller so this is a tough choice. And if chinese servos have cogging then it makes little sense to get them over diy hoverboard solution.
If hoverboard has cogging it surely can't be worse than a stepper right XD

there is no cogging in my experience - its to do with the resolution of the encoder pulses

Nice, no cogging!