[Son of Númenor]

I also see something of a parallel in Theoden's pity for Grima, which results in Saruman's forces breaching Helm's Deep. Maybe this has something to do with the negative effects of concessions Tolkien saw being made in his lifetime: the moral concessions made by his home country during the war and in industrialization; doctrinal concessions made by the church and by his fellow faithful...

The key difference that comes to my mind between the story of Beorhtnoth and the Lord of the Rings (and Beowulf, if you want another point of comparison) is that the latter is an account of a conflict between polar extremes, whereas in the Battle of Maldon there was common ground in the chivalric code and shared humanity of both sides. Gandalf challenging the Balrog is like St. Michael slaying Satan... not in any allegorical sense but in that they represent opposite elemental forces, the light standing against the dark. So thematically, was the decision Gandalf faced akin to Beorhtnoth's? No 'pride goeth before a fall' here.