None of this information was available to me at the time, and the 5.1.1 history I've only just learnt whilst composing this comment. I'd purchased the device under sharp time, budget, and information constraints whilst travelling. Budget and other limitations, as well as a market void of credible alternatives (Purism have my eye) have prevented replacement, though I loathe this device.
Google have considerable monopoly leverage, and yet have not used this to require obligations for (and permit forward use of) Android and related ecosystem services in the form of upgrade timeliness SLAs and minimum EoL requirements: this device was obsolete at time of sale, though I was completely unaware of this at the time. Instead Google have sought to perpetuate their own monopoly and interests:
https://www.theverge.com/2018/7/18/17580694/google-android-e...
It is also not capable of being re-ROMed, another fact of which I was unaware.
I'm beyond disgusted and will not and do not recommend Android to anyone.