New Formulas Simplified

Spears/Polearms have 2 type of action ,stab and swing . So does the multiplier.
To a normal attack with spear, you will probably Stab at 60% chance, or Swing at 40% chance.
Polearm is similar, 60% Swing and 40% Stab.

But the 3rd job skill ,Crusher and Fury, will force your action to 100% Swing or 100% Stab.

At your stat, casting crusher with spear deals the base damage range 5016.8~6883.

So in fact, your min damage didn't increase a lot. (6616-5017)/5017=31.87% seems to be right.

My bad. In fact, it went up from ~72% to 80%, in multiplicative conjunction with the 20% maxDamage increase.