Since that post back in Jan 2019 a good friend actually gave me an EVOC Enduro blackline backpack.
Probably one of the most advanced mtb backpacks available, tons of pockets and cool features including a spine protector anti sweat webbbing and it's seriously comfortable when loaded.
You know what it gets used for?
Carrying 14 cans of lager and a rake of weed one whole mile one evening per week. There's even room left for munchies.
Oh and the mile back home again empty at 4am. Fuck knows if it's comfortable empty but the spine protection isn't a bad idea
I still wouldn't ever do an actual mtb ride wearing it