[Kath]

The orcs might not have been as well regimented as the Uruk Hai but they were still well ordered with leaders and sub leaders (e.g. orc who looks like foam as main leader and then orc with two head that says "Catapaults!"). Also when the camera angle was from above you could see that they were arranged in pretty organised rows and columns. Then you have their secret attack on Osgiliath - all of which gives the impression that they could have developed a counter-attack against the Rohirrim without too much trouble.

I think the problem was the sunlight, the Uruk Hai should really have been able to withstand that as that was a mahor thing in their design, but the normal orcs have always avoided sunlight and so it is understandable that they were overwhelmed by it.