There is also Armored Lord/Emperor for Edelgard, if we disregard the elephant in that room.
The only difference it has to Fortress Knight is having higher HP, a bit lower defense, mildly higher luck, and +1 movement. And Edelgard having Raging Storm.
Pretty sure most of the main stacking strategies can be applied to Edelgard, with the added bonus of Aymr wrecking things. But I am not sure how much value it has in post-skip CF.