First off, what do you not like about your mid-drive.
Like said above, assist 0 will not drag when pedaling; any level of assist will not drag unless you suddenly cut the power and it will simply 'feel' draggy for a few seconds. When I have PAS I often put it to 0 on longer descents and just pedal. The only thing that's draggy is the extra weight of the e-bike. Assist one and pedaling is great for flat surfaces. More assist is needed on inclines of course.
As far as the throttle, a lot of people before they try an electric throttle think of being on a motorcycle or dirt bike, just twisting it a little and they take off about as fast as they want. It's not like that at all, at least for the bikes under 1000W. Yes, you can throttle without pedaling but you will quickly notice that unless you have 1500+W, the power and speed will fade in and out due to the terrain, even on pavement. It will not be consistent like a 20 HP / 15,000W equivalent dirt bike. What I think is interesting is that on a geared hub drive, you can PAS all day long up and down hills with no power fade, but if you throttle only up a steep paved hill, the power WILL fade. Again on a lower-powered ebike. It will fade uphill just like a lower-powered direct drive, even if it's a geared hub drive. In short, you do need to pedal with a throttle for lower-powered ebikes, mid- or hub. The throttle is there for assist just like PAS is; the main difference is that you can quickly fine tune the power better with the throttle (advantage), and your thumb has to sit there doing it (disadvantage).
Does pedaling help with speed. A little. Maybe 20%? If you throttled only at a relatively slow 10 MPH on a flat surface and added light pedaling just to keep the pedals moving (and your legs with something to do), it would boost up the MPH to maybe 11 from 10. If you pedaled harder maybe 12-13 MPH instead of 10. You don't really pedal for the speed, you pedal because that's what a bike is for, the cadence, the consistency to keep you going when the terrain changes and pedaling while you are adjusting the throttle's power output. Pedaling becomes a lot more important uphill offroad to keep the bike going; throttle only will be very hit and miss offroad, so it's usually fine on pavement but the more offroad you go the more pedaling becomes important, more so for the stability and momentum of the bike than speed alone.
Lastly, there are throttle programs that limit speed and also act like cruise control where the controller senses speed loss at a constant throttle input which tells the controller the bike is on an incline. The controller automatically ramps up power to compensate, hence the term 'imitation torque'. The controller is doing the equivalent of (anthropomorphizing) "pressing down harder" on the pedals to get you up the hill, even though the pedals have nothing to do with the increased power through the hub. It's the same result though. So yes throttle only can at least partially navigate inclines and declines by itself but even with those programs on, I personally still feel the need to pedal even if it's lightly to keep the pedals moving. It does add maybe 80-150 watts of human power, and you'd be surprised how much that 'fill-in' power helps for smoothing out the ride velocity compared with throttle only.
