Turned out to be H_SV_MAN.
I used 3 (Mid collective) to level swash.
Tried entering 2 and 4 today (Min/Max collective) and its visibly off level.
So I used 1 (passthrough) to re-level swash, then it seemed better, not much but good enough
Some very tiny oscillation now and then, overall its great!
From this vibration log, it's flying at 1700 RPM (60% Throttle). 10% less than this it becomes unflyable.
More RPM is just worse.
SK-720 shows that the vibration is better than my Warp 360 with its 4mm-thick-metal plate + foam tape mount, so I think Cube (preferred name over Pixhawk 2) just needs better mount.
Take off oscillation got better after I lessen safety level of the skid, now I have to deal with yaw blow out (see the video).