The same could be send of divine favour - that it should all in the dice rolls, or should be independent of class (qv Runequest, or the process for divine intervention in Gygax's DMG - which latter contrasts with the allocaiton of divine intervention, in 5e, to the cleric class).That's what the dice are for. Sometimes you roll well and have a hot steak. You are on your game, feeling good and doing awesome! Other times you can't catch a break no matter how well prepared you are.
A lot of this really should be done through role-playing and not limited to a class.
But in D&D divine favour is allocated to a particular class. That's what happens in a class-based game. Similarly, high level thieves have a special propensity to be lucky, barbarians have a special propensity to be angry, etc.
A contrasting example: in one of the final episodes of the Born Again sequence, Daredevil hears Captain America giving orders to his fellow Avengers, and immediately understands why this mortal man can command a god (Thor).An example occurs to me...
In The Avengers movie, Captain America gives a cop a bunch of orders. The cop basically says, "Why should I listen to you." Cap then proceeds to kick a whole lot of alien butt, then turns back to the cop. The cop turns and starts following Captain America's orders. Why? Because he is an incredibly good fighter.
Different works of fiction express differing conceptions of human relationships, and of charisma, the relationship between mortals and the divine, etc. Which is my point: the idea that the warlord raises challenging "fluff" issues is really a view about these matters.
In LotR, Faramir "can master both beasts and men" (p 840, Unwin 1 vol ed). There is also Prince Imrahil of Dol Amroth (pp 852, 855-6):
[F]oremost on the field rode the swan-knights of Dol Amroth with their Prince and his blue banner at their head.
. . .
So it was that Gandalf took command of the last defence of the City of Gondor. Wherever he came men's hearts would lift again, and the winged shadows pass from memory. . . . [W]ith him went the Prince of Dol Amroth in his shinging mail. For he and his knight still held themselves like lords in whom the race of Numenor ran true. . . . And then one would sing amid the gloom some staves of the Lay of Nimrodel, or other songs of the Value of Anduin out of vanished years.
'Amroth for Gondor!' the cried. 'Amroth to Faramir!'
. . .
So it was that Gandalf took command of the last defence of the City of Gondor. Wherever he came men's hearts would lift again, and the winged shadows pass from memory. . . . [W]ith him went the Prince of Dol Amroth in his shinging mail. For he and his knight still held themselves like lords in whom the race of Numenor ran true. . . . And then one would sing amid the gloom some staves of the Lay of Nimrodel, or other songs of the Value of Anduin out of vanished years.
In that passage we also see bardic inspiration (and nothing to do with magic, except the everyday magic of song and sincere conviction) as well as Gandalf.
Gandalf is also an inspiring figure. He inspires Aragorn and Legolas, among others, at Helm's Deep (p 565):
'Behold the White Rider!' cried Aragorn. 'Gandalf is come again.'
'Mithrandir, Mithrandir!' said Legolas. 'This is wizardry indeed. . . .'
The hosts of Isengard roared, swaying this way and that, turning from fear to fear. . . The White Rider was upon them, and the terror of his coming filled the enemy with madness.'Mithrandir, Mithrandir!' said Legolas. 'This is wizardry indeed. . . .'
Gandalf inspires, too, in the final battle (pp 984-5):
All about the hills the hosts of Mordor raged. The Captains of the West were foundering in a gathering sea. . . . Aragorn stood beneath his banner, silent and stern . . . but his eyes gleamed like stars that shine brighter as the night deepens. Upon the hill-top stood Gandalf, and he was white and cold and no shadow fell on him. . . .
Then all the Captains of the West cried aloud, for their hearts were filled with a new hope in the midst of darkness. . . . But Gandalf lifted up his arms and called once more in a clear voice:
Then all the Captains of the West cried aloud, for their hearts were filled with a new hope in the midst of darkness. . . . But Gandalf lifted up his arms and called once more in a clear voice:
'Stand, Men of the West! Stand and wait! This is the hour of doom.'
Just as the warlock, sorcerer and wizard all overlap heavily in trope, but give different approaches to the same archetype; and just as the war cleric and the paladin overlap heavily in trope, but give different approaches to the same archetype; so the bard and the battlemaster don't exhaust the ways in which an inspiring battle captain might be expressed mechanically.