I have a headcanon about Stenn.
When I first read about him, my immediate thought was of Gorig, the Phyrexian spy who brought down Serra’s Realm. They both take a militant stance against Phyrexians in their midst, and are ruthless in getting rid of supposed Phyrexian sleeper agents. They both inserted themselves into positions of authority to deal with the Phyrexian threat, while secretly helping Phyrexia. Also, they both have goatees.
Maybe it’s just me, but it almost seems like Gorig and Stenn could be the exact same person. Given their similarities, I hypothesize that the Phyrexians based Stenn’s design on their memories of Gorig. We know that Kraynox, who is one of the black-aligned Steel Thanes, has created a layer of oil and uses it to learn about Phyrexia’s history; it seems plausible that he or another Phyrexian (I’m sure Sheoldred could either steal Kraynox’s plans, adopt his tactics if it suited her, or force him to help her somehow) could have studied the fall of Serra’s Realm and gotten the idea to make a new version of Gorig for the Phyrexian conquest of Dominaria. And Phyrexians aren’t exactly known for their creativity—if Gorig worked so well for old Phyrexia, why not recreate him for a new era?