Why would a ship need stairwells if it has ladderways? Just curious.
The ship really OUGHT to have some stairwells in various places. We never saw those in TOS. We saw LADDERWAYS, but no stairwells.
Ever try to carry equipment up or down a ladder?
Steps really only require your feet (although it's NICE to have a handrail, just in case).
Ladders require both hands and both feet... though it's POSSIBLE to climb with just one hand (but both feet) or just one foot (but both hands) it's damned difficult, and pretty dangerous to boot.
Of course, if you have an over-the-shoulder pack for whatever you're carrying, you can get by with just ladders... but if you need to have ANYTHING in your hands... ladders really aren't a good idea!