There's no way to remap the power key during recovery..
If you can control everything from pc without the power keys then I'd recommend you to open the back-cover and disconnect the power and volume keys from the motherboard.. Its not that hard just be careful while disconnecting..
Follow any simple tutorial on YouTube for reference (I searched.. there are ...
I've found another potential cause for Charging slowly which I didn't see in any previous answers.
My phone (Moto G7, USB-C charger) had debris in the charging port which made it difficult to charge. The connection was loose, and when it charged at all, it would often indicate that it was Charging slowly.
Cleaning the Charging Port
In my case ...