"Would people ever say that they knew how it felt to have no ability to walk,
if they were not so disabled?"
Strictly speaking, phenomenologically, you are correct : we can never fully
know another's experience.
However, I would say that someone who lived with such a disabled person, was
their companion, helper, friend, while not knowing precisely what the struggle
was like from the inside would nevertheless have a very good idea about what
the day-to-day struggle was ...
We may not have a certain experience but we may be friends, lovers,
companions, relatives with people who do, and depending on our level of
involvement and empathy may have a rich understanding of the texture of that
experience.
That should never be understood as an equivalency, but it is nevertheless
important.
(un)leash