Without showing emotion I don't see how you can show personality. I don't mean extremes, even something little like a grin in conversation or a frown or anything other thane a stone emotionless face. The only glimpse of emotion I have ever seen from Cain is when he raised his arms and fell to the floor after he beat JDS.
I dunno, maybe it's just me sees it like that?
The level of speach, the tone, all of that can show you a person's personality. Not just face microexpressions. The reason I say that is because if you judge based on microexpressions, then you can be twisted or in other words fooled. These can be trained to show something other than what is truely behind that face/person
You can read about deception/deceivement, and stuff like that if your interested.
Fedor having no personality was/is a myth in my opinion, the truth is he was just your ordinary family guy that lived next door who would rather go for a walk with his wife and kids at the park (like Cain). Then he would walk into the ring, calm and collected, nothing flashy, not ripped like some of the juice heads (instead a little chubby) and just proceeded to slay everyone once the bell rang.
liked that BOOM.