Pressed, fabricated or forged, if cast was strong enough you would not need a bash plate as cast cases would be strong enough. It's about elongation before it breaks.
In parts like cast frame members or swing arms you have well defined forces below the yield strength of the material.
Most impacts into the sump guard cause forces well in excess of the materials yield strength. You need a material which is ductile on the one side (it absorbs energy by deforming and allows a high amount of elongation before it tears) and has good shear strength on the other side (a rock will not tear a triangle shaped hole).
I found sump guards from 4mm 5083 sheet to work very well and the sheet is readily available and quite corrosion resistant.
The putty soft architectural grade stuff is useless.
A cast bash plate will crack and shatter just like eth engine you are trying to protect.