You don’t actually add 50% more damage. You only add 50% of your physical attack as damage. I.E, I do around 2K damage on zinutekas and have 380 physical damage. With knockdown on, I’d do extra 190 damage. It’s not really that worth it Sp-wise in my opinion.
Monstrance’s DEX buff also doesn’t scale with Skill points. Leveling that skill is just a waste of skill points.