Using my own compiled coreboot + kernel + rootfs didn't yield positive results. My Switch is yet again displaying the battery discharge issue. Funnily enough, I thought for a second that I damaged the right Joy-Con rail pins or the USB-C port, or that I shorted some pins I shouldn't have, because I wasn't being able to enter RCM, and my laptop was instead making the Horizon OS boot. I was beginning to worry when I noticed the battery problem yet again.
@Shadow LAG Since I've been able to replicate the issue not once, but twice, using different rootfs, are there any kind of tests you may to perform? Just let me know.