This is something of a tough assignment, but don't get too caught up in finding the one right answer. I'll try to help with the Stevens' poem.
The Stevens poem offers a more conversational or colloquial tone which is in keeping with the poem's attitude toward death, which you correctly identify, I think, as one of inevitability. The statement of the poem seems to be that death for a soldier is part of the nature of being a soldier. There are no suprises. It is like autumn, an inevitable consequence of the earth's movement around the sun. This is a poem of passing, spoken in passing, concerned with passing and using images of clouds passing.
In this poem we can see a use of repitition and some irony (this is a poem about how the death of a soldier doesn't really get any attention, yet the poem is giving attention to the death of the soldier). We begin to see in this irony some of the complexity of the poem. A further complexity comes in the arbitrary nature of the difference between the "three days pomp" of a non-soldiers' death and the lack of that pomp for the soldier.
We can read this poem as suggesting that all people are like the soldier, death is expected and inevitable. We are all caught up in the exact same fate. Yet there is an implication that the "three days pomp", the funeral rites, etc., given to non-soldiers are indicative of a failure to connect our own fate and nature to that of the soldier. There is a subtle suggestion that we should all see our own fate as identical with the soldier's and see it as part of our nature too, but we don't.
Identifying the tone of the poem as jaded bitterness seems to be overstating things and kind of missing the point. This poem is not about soldiers, it's about the human condition.