Your first link is temporarily not working, but you're arguing against the wrong point anyway. I accept everything you said to be true. Not depleting the battery below 20% is not because low states of charge are bad for the battery. You have already made a convincing argument that they are not. It is to keep the depth of discharge lower, which is known to be good for battery longevity, though I currently don't have a primary source for that right now because I'm not on my computer. You could get the same benefits by charging from 10% to 70% or 0% to 60%, and in those cases that might actually be better for the battery, but people like having a buffer rather than pulling up to the charger running on sparks, so that's why 20% is the recommendation.