Good questions and points.

The army captain has no particular character flaw that jeopardizes the success of his mission.? He’s a competent fighter and leader. The proof is that he just led a successful campaign to defeat the Cheyenne chief. A war in which atrocities were committed on both sides.

So when he’s ordered to reverse roles and protect rather than fight his erstwhile foe, he initially refuses to obey. ? But he’s on the verge of retiring; if he doesn’t obey, he’ll be expelled and won’t get his pension.? So he salutes and saddles up.

The reason the captain must escort the Cheyenne chief is because the journey home for the Cheyenne is through hostile Comanche tribal lands. Hostile for both the captain and the chief;? the Cheyenne and Comanche are enemies.

So maybe something like:

In 1892, an army captain reluctantly obeys his orders to escort his erstwhile bitter enemy, a dying Cheyenne chief, through hostile territory so he can be buried in his tribal lands.? (31 words)

Not the strongest logline with irresistible sizzle, I grant? you.? But the writer had the advantage of already being an industry insider with a proven track record as a writer and director. He wasn’t an outsider who had to deploy a logline to cross the castle moat, breach the gates, overcome the guards to get inside the Biz, get his script read — and produced.? He could promote the script through his agent and his industry network.