>>12358>taking the Homulabyrinth at face value
Outside Homura's labyrinth, Mami can only create one type of firing weapon, a simple to make single-fire musket from ancient times. If I remember correctly, the cannon is the same single-fire weapon, just bigger.
Everything else is only in Homura's labyrinth, so the giant cake-tea tank-cannon is just Homulabyrinth magic summoning up whatever Mami thinks is cool. Stuff like decoys are the same labyrinth at work. Pretty much all of the Homura vs Mami fight is the drama theater of Homura's subconscious. The real Mami can't move or fight like that, nor does she sneak ribbons onto friends on a whim, nor does she have infinite invisible ribbons, nor does she have decoys, etc. It's just Homura vs Homura's labyrinth more than anything else.
TL;DR: Everybody is getting played by Homura's AI