Try it for yourself some time. Run or walk up a set of stairs in a tall building (or hillside if they do that out west). Note how far you get before feeling it, and/or the time to that level. Now find a hill of similar height an climb on your bike. Assuming you have the gearing, I'll bet that the time and effort to the same height will be very close.

Years ago, I lived on the side of a decent hill that the road climbed via a grade with a switchback. It also had stairs built up the fall line (a common feature in hilly NYC neighborhoods). Friends and I would hold bike/foot races to the top, and learned that the same people won regardless of how they did it.