No HA mfg would be dumb enough to require using their charger AS THE ONLY MEAN to complete an ON/OFF cycle of their rechargeable HA. Of course it’s ONE option to do it, but there is always a manual option as well if you read the instruction manual carefully enough.
If it’s true like you said that you CAN ONLY use the charger to cycle ON/OFF the aids and there’s no other way (and I really doubt that it’s true for any of the rechargeable aids), nobody would want to buy that brand’s aids in the first place. I know I wouldn’t. That would be considered a design error, not just a lack of feature.
Speaking of the Lumity manual that you mentioned, I looked it up and found the following → The first screenshot below for the Lumity on page 21 of its manual tells you how to turn on/off the aids manually without needing the charger. Maybe putting the aids into the charger and removing it is an option to cycle power the aids, but I’m sure it’s not the ONLY way.
The second screenshot below is the instruction on how to turn ON/OFF the Oticon rechargeable hearing aids manually without the charger. And of course it’s also designed to turn off when put into the charger and turn ON when removed from the charger.