A possible change then since March 22nd, 2019? That's the date that a guild member from CAH posted that YouTube video. They play OSI on the Chesapeake shard. You can see they are able to move 1-2 tiles closer after killing the orcs by the cannons (again, I'm referencing 1:20 in the video.) It doesn't mean that ALL cannons stop firing, just the ones no longer controlled by orcs.