It would be cool if specific animals like elephants or rhinos could be commanded to attack another player’s structure to help siege. As well add this to thralls so if you want to spend the resources they could use fire orbs and explosive arrows on structures too.
I assume they could damage T1 only though, also similar structures made of weak ingridents (for example partially animal pens, stables etc) aswell as can demolish Pallisades but they would take alot of damage in return which would let the defending side kill them easier. I doubt an animal is able to demolish a T2 wall.
A group of armored rhino or armored elephant riders btw could be able to crush a group of mounted horsemen if they attack as strict formations at a narrow spot. Not possible at the open field where other mounts can maneuver very fast.
Once again the weakest side of military animals was caltrops. Caltrops were used against charging horses and charging elephants in historical wars.