But without a nicely balanced position over the bike, the rest of this will make no difference whatsoever. Ask any hot climber how his or her arms feel after some really steep pitch and the response will be, exhausted. This is one of the major differences between road riding and mountain biking, the degree of involvement of arms and shoulders. The entire body for that matter. Mountain biking tends to be a full body workout while road riding concentrates much more on the legs.
Steep pitches are really just isometric exercises with the arms opposing the legs.
But how you pull back is critical because if you pull back and up, which is the normal pulling action, you're accentuating the unweighting of the front wheel, which is exactly what you don't want. Again, a slight detour into the realm of physics is necessary. Any time you pull back on the handlebar, which is obviously connected to the front wheel, there will be a vector force that either tends to lift the front wheel off the ground or presses it to the ground. Or has zero effect, neither lifting nor pressing down. If the pulling angle is parallel to the top tube, the vector force will be neutral.