Is root ownership inherited in shell scripts? (rsync via ssh permission denied)
I'm going to attempt a self-answer although it is something of a Frame Challenge / XY problem situation.

I never found out what exactly was the problem with the configuration I had, however I was able to get what I wanted, ie fully integrated command-line ssh / rsync / bash scripting etc. by installing CyanogenMod 11 on my Samsung Galaxy S3 GT-I9300, as these and more command-line tools come as standard and are evidently properly set up so as to avoid the odd problems I experienced on my previous configuration.