Gobias - go back and read the book. The riders pour through the shield wall. Theoden gazes across to the ongoing battle and: "...he seemed to shrink down, cowed by age..." but then the wind changes.. "light was glimmering. Far, far away, in the South the clouds could be dimly seen... At that same moment there was a flash, as if lightning had sprung from the earth beneath the city. For a searing second it stood dazzling far off in the black and white, it's topmost tower like a glittering needle; and then as the darkness closed again there came rolling over the fields a great boom.
At that sound the bent shape of the King sprang suddenly erect. Tall and proud he seemed again; and rising in his stirrups he cried in a loud voice, more clear than any there had ever heard before:
Arise, arise, Riders of Theoden!
Fell deeds awake: fire and slaughter
Spear shall be shaken, shield be splintered,
A sword-day, a red day, ere the sun rises!
Ride now, ride now! Ride to Gondor!
I don't actually see how that is so different from what happened in the film. The Rohirrim arrive on the field and Theoden looks down at the Orcs and the look he gives in that moment is the line "He seemed to shrink down, cowed by age" Now I'm not saying he shrinks down. But that look is the films equivalent of that line. He looks down and sees what they are up against and you can see in his eyes that he knows, or thinks he knows, they can't win.
The "flash of lightning" bit never happened in the film. In the book that is what shakes the King and makes him go into his speech. In the film, his own determination wins out against his pessimism and that shakes him into battle mode. He gives his bannermen their orders, which he had done prior to arrival in the book, and then goes into the speech. From that moment their is no morbidity at all, other than the Rohirrim chanting "Death!" which was lifted from a little further on in the book and was a great decision in my mind. The chant of death shows the Orcs that they are not afraid of what is to come. They ride happily to death for honour.
Now, of course there are changes there, but I don't see how the overall mood of the scene is that different between the two. There isn't rampant morbidity in the films version as you claim.
Peter Jackson's retelling of the charge was definitely not perfect, but it isn't as far from it as some make out. But I still think the music fit beautifully. It had trumpets and whatever you expect from a cavalry charge mixed in with touches of music that had defined Rohan since the second film. It wasn't just a cavalry charge, it was the charge of the Rohirrim, and I think it conveyed that well. It starts off with the violins etc, but grows to a crescendo. It gets faster and louder as the Rohirrim get faster and closer to the Orcs.
My biggest problem with that scene wasn't the music. It was Theoden riding along the front of his host shouting "Ride now!" and no one moving. Surely that makes no sense. He shouldn't have been shouting that. He should have been shouting something different. When he shouts "Ride now! Ride now! Ride to Gondor!" in the book, he immediately takes a horn and blows it asunder and they set off. In this, there is about a minute between him shouting "Ride now!" and them setting off. It's silly.
I haven't contested that the film version was different. I'm contesting that there was no tragedy in the Ride of the Rohirrim and that all any of them cared about was the honour they would receive, dying in battle.
"So it was that in the gathering gloom the King of the Mark made ready to lead all his Riders on the eastward road. Hearts were heavy and many quailed in the shadow. But they were a stern people, loyal to their lord, and little weeping or murmuring was heard, even in the camp in the Hold where the exiles from Edoras were housed, women and children and old men. Doom hung over them, but they faced it silently."
"All the lands were grey and still; and ever the shadow deepened before them, and hope waned in every heart."
These quotes are from before and during their ride to Gondor, but they are still relevant to the telling of the later scene. The impending doom didn't cease to exist just because the Rohirrim were about to charge. These men thought their culture was going to be wiped out if they failed, and they didn't think they could win.
The rest of the quotes you made were during the battle itself and I don't see how you can say that was morbid in the film, other than all the obvious death that was happening. Those quotes don't pertain to the bit of the film or the book that we are talking about.