When is a poem not a poem?
When it's a collection of words yoked together by formal rules alone
Six Short Poems (4) Du Fu A sudden rain The slanting sun sprinkles turns about the feet the waist of the creek of the tree The yellow birds The white fish stand in pairs leap on each side of and turn over a new leaf and a nest 杜甫 绝句六首·其四 急雨捎溪足，斜晖转树腰。 隔巢黄鸟并，翻藻白鱼跳。
The feet of the creek are its lower reaches.
Here, I think Du Fu is pushing his parallelism to the extreme. He has abandoned visual rhymes in favour of something that approaches a pun. Slanting sun and sudden rain don’t have anything to do with each other; they just fit the formal parallel pattern. Similarly the feet of a river and the waist of a tree don’t share anything except this shared metaphor of human body parts applied to something in nature. The actions of standing in pairs and leaping are utterly disparate, and in fact the verb 并, for being in a pair, is used in an unusual way. It’s like Du Fu is showing off how he can shoehorn different things together simply through the form of his poem.
You are correct that this poem paid particular attention to parallelism, in fact it could be argued that you understated the degree of parallelism. For example, the grammar of every word of the first two and last two lines are exactly parallel. The first and second lines are, as I read them: adjective, noun, verb, noun, adjective; the third and fourth are: verb, noun, adjective, noun, verb. Meanwhile, the contents of the parallel words are instead meant to contrast, as in the "driving rain" and "rays of the setting sun."
And the tonal pattern of the first and second, and third and fourth lines of this poem, as was the practice for this genre, are mirror images of each other. During the Tang dynasty the 平仄 were probably like this:
仄仄平平仄
平平仄仄平
仄平平仄仄
平仄仄平平
The grammar is strictly parallel, the contents contrast, and the tones are perfect mirror images. This poem attains the highest standard for 五言绝句.
A famous Du Fu scholar of the late Ming dynasty appreciated the juxtaposition of the driving rain and rays of the setting sun. He wrote that it conveyed the immediacy of the changing landscape. And later poets like 陆游 used the exact same words in exactly the same kind of parallel construction. For a poet like Du Fu, I think that combining apparently disparate elements in this manner suggests that he saw poetic connections that people don't see today.
Are you deliberately merging the parallelism at the end there? Should the last two lines be read as part of both parallel sentences? Maybe put them on one line if so to indicate that more clearly.