This fire from Isengard bit really does make the viewer wonder
Why didn't they just make a bunch of bombs and blast the place to smithereens? I guess that's a problem with fantasy.
And I think this would have been a perfect opportunity for Gimli to really prove himself as a dangerous warrior. He just seems to wander about the field not doing much, or sticking his axe into an already-prone Warg (incidentally, those Wargs are a shocking reflection on the most noble race
).
Legolas got his
"Look at me! I'm killing 100 men all by myself!" moment in RotK; Gimli could have got a bit of a rub in TTT.