why did beerus guard creatures battle axe? Because it seriously damage him. Why did that laser beam pierce Goku body? Because it doesn't relate to ki. Why didn't vegeta just punch a whole through megaton? Because it was very dense metal. So imagine if megaton was made out of spikes, would will vegeta do besides shoot ki blast? Nothing. Goku body isn't made out of metal, they need to concentrate ki inside there body on a specific area to harden it. Can Goku do that in his fight with morrigan who reared apart photos with ease? No. Will her tentacles be visible for Goku to dodge? No. Its hidden out of his sight. Did you notice in the fight between demitri and morrigan that demitri was on the defensive the whole time?( he has shields, Goku doesn't have the same luxury). How will Goku defend? Morrigan can just dodge his energy blast and close the distance. She is flying at speeds of Mach 5, she's faster than a jet.