There is nothing like PAS-only in the premium mid-drive motors. A mid-drive motor only pays the attention to the product of how hard you push your pedals (torque) and of your pedalling rotational speed (cadence). The product is called "pedalling power" or "human power input". In given Assistance Level, the bike controller multiplies your pedalling power by so called Boost Factor, and such mechanical power of the motor (combined with your own) is transferred to the rear wheel.
Meaning: "Mashing" pedals times slow cadence would give the same pedalling power as "spinning the cranks" times (less energetic) pushing the pedals. You won't get more workout by staying in a high gear; you're going to damage your knees by doing so. If you learn spinning the cranks faster but with less of pedal pressure (in a lower gear), you will deliver exactly the same pedalling power to the system with the same effective motor assistance. And the same number of calories burnt.
Spinning the cranks has many health benefits. It is also good for the drivetrain (less wear). Moreover, mid-drive motors are more effective if your cadence is above 70.
My favourite show that I am often giving to my traditional cycling mates is this:
1. I ride at a slow cadence in Eco
2. Then I dramatically downshift
3. Then I spin the cranks.
I am able to deliver so much power by doing so I simply disappear at distance -- without increasing the assistance! (On my last Sunday group ride, I managed the cadence of 135 but cannot maintain it for long).
View attachment 116223
My show. The power indicated here is the pedalling power.