Pedal assist systems (PAS) generally work using cadence sensors (the PAS turns on after you start rotating the cranks) or torque sensors (the PAS turns on when you apply pressure to your cranks). Some mid drive motors use a combination of both, but Aventon doesn’t use mid drives.
Cadence sensor systems can give you an abrupt feeling of the PAS system turning the motor 100% on or 100% off, with no in between. That’s in fact generally what’s happening with cadence sensor systems. The PAS levels generally don’t provide different ramp ups of power, all they do is provide different max speed cutoffs. If the motor and programming is well matched to the weight of the bike, the all in on/off sensation may not be that noticeable.
Torque sensor systems provide a more natural power delivery ramp up based on how hard you’re pressing on the pedals (how much torque you’re applying). It generally provides a more natural feel, and you don’t need to start pedaling on your own before it kicks in as it senses the pressure before the cranks start rotating.
I’m sure there are a lot more technical explanations with varying degrees of subtleties from system to system, but generally speaking that’s how I would summarize the primary differences.