You know what's worse than computers? Portable computers that run smartphone OSes. Not only are they approximately 5 times as boring as proper computers, but all the information about them is from semi-literate millennials on horrible web forums. Those guys take cargo-culting to a whole new level, and you can't just exclude 'Ubuntu' from your search terms to filter out the idiots like you do when seeking enlightenment for grown-up Linux problems.
Anyway, having jumped through some nasty Windowsy hoops to flash the recovery on my Galaxy Tab S2, I've hit a wall by discovering - about 3 iterations of mkfs.ext4 too late - that there are in fact two different (and innacurately labelled) flavours of LTE 9.7" Galaxy Tab S2, and that SM-T819 (AKA gts210ltexx) is not the same thing as SM-T815 (AKA gts210velte). Bastards.
I've managed to un-brick it and gain root access, but unless either a) LineageOS starts supporting the newer model or b) I miraculously find myself arsed to do all the work myself, it looks like I'm stuck with the invisible Samsung quick settings GUI for a while longer.
Even when this stuff goes right, it's unsatisfying in exactly the way that ball bearings aren't.