What controller does the Alta use?
Find machines that have the characteristic you want and see what controller they use.
Sevcon controllers are extremely programmable, so things like lag can be programmed. However anytime you are using a controller that is torque based, there is always a feedback loop between motor current and the PWM used, and the throttle is the control value. This can be tuned to minimize lag time, but it won't be zero. Expect to spend a lot of time tuning the system.
To make a lag free torque altorithm the system must be fully characterized and then a predictive algorithm used to avoid feedback delays. This would make the system complex to set up and not something that could be sold to the general user.
Simple square wave controllers can have effectively zero lag as they just read the throttle convert it to a PWM value and set the registers, so the delay can be microseconds. From there it is just the inductive ramp up of the motor current. They add filtering lag to their algorithm to make it smoother, otherwise blipping the throttle can make uncontrollable thrust. Truly zero lag may not be controllable, even by an expert.
So the trick becomes programming just the right altorithm and tuning it, rather than truly zero lag.