Hello,
this problem is very often caused by mechanical problem in the rotor head. Axial bearings are the main problem when there is a lag.
Please try to disconnect push rods and move with the blade holders by hand.
Do you feel any counter-force?
If so, it is wrong. It should be absolutely smooth. Any settings in the unit will not fix it.
Regarding these servos, they are unfortunately not too good for FBL usage. They have no coreless motor, so they can fail much sooner than other. But it can of course fly very well with them too. But if you want to make a big upgrade, I highly recommend MKS DS95/DS95i or at least DS92A+ servos. The flight characteristics are uncomparable. But the price too
Very cheap but good upgrade is TGY-306 servo.
But this is just for the future.