So let's set the scene first:
Back at the gates the orc bodies continue to pile up as they try to break down the gates with a battering ram. Gothmog walks up to them.
GOTHMOG: What are you doing you useless scum?
ORC: The door wont give. It’s too strong.
Archers continue to kill the orcs who are piling up in heaps.
GOTHMOG: Get back there and smash it down!
ORC: But nothing can breach it!
GOTHMOG: Grond will breach it!
So you squander lives feebly fumbling against a door, can't breach it, try to squander more lives, argue with a soldier about it, pause to think and remember "oh yea, what about that battering ram we've been dragging halfway across Middle Earth, you know, that legendary one who's single purpose is to break down hard-to-breach doors? Let's try that one!"
Why not start with Grond in the first place?