I didn't realize I had been navigating my bike incorrectly on stairs for so many years by simply rolling it up and down the stairs just using the wheels while I push it and stabilize it....lol
My commuter with all the racks, luggage etc must weight over 50 lbs, but I like my Peugeot MTB to be heavy as it is more stable in inclement weather.
No way would I lift a bike by the rack, it is indeed made for a downward load.
I am also tall and have very steep and narrow stairs, If my bike is loaded with groceries etc making it even more heavy I brace my body against the wall or stair rails and take it slow.
If you have an outside balcony you could always rig up something like this:
https://www.youtube.com/watch?v=TANb2p-HwlE
Seems to work for this guy...lol