Ok to shift middrive under low power?

I used to shift my middrive e bike by letting off the throttle completely, but that made shifting pretty slow. I've been trying recently shifting without letting off the throttle completely to quicken things up. I just reduce my throttle output to 15-20% and shift. Is it really that terrible for the drivetrain? It feels a lot smoother shifting like this. I also have a torque throttle so I don't have the issue of a PWM throttle randomly applying torque. 15-20% throttle would only be about 500-600 watts.

It is ok under high rpm and low torque.