What trigger throttle do you have right now?
Is it the QS-S4?
I think what you are experiencing is a bit of both and not sure that swapping out the throttle unit is going to help much.
Both the throttle itself (particularly if it’s a trigger) AND the controller contribute to the “jumpiness” of the scooter.
The trigger throttles are quite non-linear and have a significant “dead zone” as you start to squeeze them down. The second aspect is that the controller (beefier component buried in the deck) has a bit of delay before it starts putting real power into the motor. Part of this is that on most scooters the controller has to figure out which way the motor is starting to rotate as it puts out power and apply a phase offset to it going forward.
The combination of this trigger deadzone and controller phase adjustment means that you squeeze down on the throttle continue to feel nothing until maybe you’ve hit 50% throttle until all of sudden you’re being launched.
I think if you swapped out both the throttle and controller for one of the more premium units (like those we see in esk8), you might be able to solve the problem, but this would be a bit like doing a brain transplant on your scooter and significantly expensive.
I would think doing what you’ve already done: dialing back power/initial torque and turning down the regen would get you about as good as you can get with the lowest level of effort.
If you do end up going into more serious scooter hacking, keep us updated on it!