meanwhile Gandalf makes a cavalry charge down a waaaaaay too steep hill towards the aforementioned pikemen

The Battle of Helm’s Deep is full of very obvious errors. There is an awesome Dutch historian, Roel Konijnendijk, who trashes movies for fun that talks about it:

https://www.youtube.com/watch?v=xPGdOXstSyk

My favourite one is when they are shouting orders to eachother. There is no way for the Elven archers to hear Aragorn’s commands, or for Aragorn to hear Theoden’s fallback order.

He had sappers. And yeah Pike beats horse.

Wise. A wizard.

Not exactly a very experienced war lord

Maybe the walls finished constructing while he was sending his troops across the map. Happens to the best of us.