The theme of "Literature and Writing" is sort of flying under the radar in this poem, but we think it's important. The whole point of this poem is to gently mock the clichéd love poems written by other authors. The speaker isn't actually making fun of his own lover so much as he is pointing out how ridiculous poetic comparisons can become. In that sense, this is a poem about other poems as much as it is about a particular woman with frizzy black hair.
As he gently mocks traditional love poems, the speaker manages to maintain a light tone. This playfulness makes it easier for him to turn the subject back to true love and finish the poem on a sweet and cheerful note.
Although it is meant to be a parody of romantic poetry, Sonnet 130 misses the fun of those other poems. By ignoring the playful nature of those exaggerated comparisons, our speaker ends up being the one who sounds like he isn't getting the joke.