Even though both poets show that they do not agree with war, they both express their point of views in different ways. Wilfred Owen actually fought in the war, so his poem is a lot more detailed, whereas Thomas Hardy did not go to war, so his poem goes into much less detail, maybe signifying his inexperience in war.
While reading ‘Dulce Et Decorum Est’ you get the feeling that the words are very heartfelt and the excessive detail suggests to you that Wilfred Owen did experience this himself, which makes the poem all the more meaningful. On the other hand, ‘The Man He Killed’ is a somewhat calmer poem – but still delivering the same idea that war is wrong. This idea may not come across as strongly as ‘Dulce Et Decorum