It depends on what you are using.
I have experienced riding two e-Assist machines.
1. The first was a very popular Bafang BBS01 mid-drive conversion on a two-wheeler without fitting the throttle. The level of assist between none and maximum can be customised to 1-3, 1-5, or 1-9 levels with 2, 3, and 5 being middle of the range in each case. As it is correctly termed a Pedelec, without the throttle, there is no assist unless pedalling - except for a push-button walking assist mode. Assist can be customised to cut out at anything between about 13 kmh and 39kmh to keep it legal. A later throttle fitting and fitting to my Warrior, showed 17kmh with the throttle although I can't confirm the customising settings.
When riding, there was no jerkiness experience with any level of assist. The assist does not start until the pedals have rotated about 1/4 turn. Yes, you can feel it when it kicks in but it seems to be softly applied, probably to prevent severe jerkiness. The manual makes mention of torque sensors in the pedalling system that must modulate the power applied relative to how hard you are pedalling. The assist also continues for a second (or two?) after pedalling stops. There is a switched brake lever option but I have not got that fitted to the trike. It is a little unusual to be pedalling, even counter intuitive, while braking. As the assist stops when you stop pedalling, there is some redundancy is switched braking. A local bike shop told me that they don't always fit them. I didn't fit them as the final resting place for the assist will be on eLecTricks or maybe there be a new purchase for that role.
2. The second experience was with a cheap e-assist bicycle that my wife purchased. This is not as sophisticated as the Bafang. The whole bike cost less than the Bafang conversion and drive is applied via a rear hub motor but that is not the only difference. I hate the way the assist is applied. Yes, it has a number of selectable levels but the application of the assist is nowhere near as smooth. In fact smooth is probably not mentioned anywhere in any of the paperwork. If it is, it shouldn't be. Whatever the level, it seems to be either on or off (jerky) and consequently seems to be either accelerating when it cuts in or decelerating when it cuts out. It is horrid and so is the hub wine.
So, there you have a comparison of e-assist. It all depends on what you are using. Of course, if you are just making up an electric drive, it could be a totally different ballgame - depending on the electric control. For example, many electric motors designed to assist us in various machines do't have a need for "soft start". The are either off or on. Check out what you might be getting, first.