Simi yi was one of wei's greatest military advisors
And even planning the battle at shiting 3years in advance he still lost to wu forces despite having more personel
But that doesn't answer the initial question. if you knew there was an enemy who did have a chance of upsetting a plan you have wouldn't you killing him? personel or not.
The inquisitor isn't some King of troops. He is literally the only person able to stop the Elder One's Tears. that isn't thinking oh it can never happen. oh i will never see him
Here is an example. say you are immortal to any attack, not sword or gun could kill you. but there was ONE dagger that could kill you, just a regular dagger. wouldn't you destroy just because it is the only one that can destroy you, and it doesn't mean someone will use it, but you eliminate the possibility of someone using it.
This isn't some king thinking oh hey he just is some dumb lord, ill let him live. this is the one guy who can stop you, small or not.
And if he isn't from the getgo trying to kill you after you close the first tear. why is that? i think its because its not his end goal. what ever that end goal is. it isn't to have all these tears everywhere open, so he just doesn't care so much. if he was trying to flood the world with demons, wouldn't he at every moment be attempting to cause more tears, and place where they would be useful. not random places like forests away from villages? wouldn't you make tears all over Denerim and such.
And now i'm even wonder why isn't he? a distraction maybe? i really don't know, i'm spit balling this theory as i go.