I think I'd rather hook/unhook a pannier that many times, rather than pull a backpack on/off my back that many times. Maybe it's a muscle memory thing, what your body gets used to. I've been using a pannier to commute for decades, now it's just second nature.
Dude I work with bike-commutes, but like me, takes the bus on certain weather days. On those days, he uses a messenger bag. He can't stand backpacks. I'm just the opposite. It's definitely based on what we grew up with.