Besides the wildfire, Tyrion's strategy was odd (can't remember exactly how the book did it)
1. Why send Dog et al., outside the walls to fight? Has anyone in the history of warfare left a position of protection to fight in an open field?
2. The wildfire was good, but he completely missed setting up entanglements that would have kept landing boats off the beach.
3. If the Mud gate was a weak point, add a small moat?
All of this does not matter, just thinking