im speaking from historical fact. if i dont know anything about a topic, i dont post.
in kung fu many things turns out not to be what you expected.
lances and sword cavalry charge directly into the flank of a spear square. guan dao rides alongside, not into, the spear square and "shave" off enemy soldiers. guan dao will mow down multiple people in one pass.
guan dao is shorter than the lance, it can cut him. guan dao is longer than the sword, it can stab him.
you have to understand that guan dao was used before firearms, in the age of heavy armor and heavy weapons. it means soldiers at that time didnt have to block or parry, they just keep swinging their weapons.