Why isn't the arm attached OVER the stump? This is Old Republic technology..maybe they couldn't attach it directly to the stump? Remember, Haazen got his wounds in the Great With war...which goes even further back.
It's just that the mass collection of possible evidence is...strange. We don't know what happened with Sions eye...maybe he put someone else's in his own socket after his artificial one was destroyed?
And for change of behaviour...Malak and Revan changed. Nihilis wasn't norn as a destroyer of worlds...I think tragedy or other stuff can change people