Prophecies are tricky because they are often ambiguous. In theory, Arya could still take out Cersei, if say, Jamie or Tyrion dies elsewhere, by using their face.
I like that little pet conjecture, because it would mean a ton of Cersei's historical paranoia regarding Tyrion is completely unfounded and misplaced -- which is a core feature of her character. She couldn't imagine Jamie doing it (although, maybe just now she can)-- so it HAD to be Tyrion all these years. HAD to be.
If it was neither, well, haha.
I like that little pet conjecture, because it would mean a ton of Cersei's historical paranoia regarding Tyrion is completely unfounded and misplaced -- which is a core feature of her character. She couldn't imagine Jamie doing it (although, maybe just now she can)-- so it HAD to be Tyrion all these years. HAD to be.
If it was neither, well, haha.