I need help writing an argument that supports or refutes the claim that complex poems are superior.

No type of poem is inherently superior. Various types of poem can be well or badly written within the context of their own genres and audiences. 
Alexander Pope, for example, wrote a two-line poem that was inscribed on the collar of a dog he gave to Frederick, Prince of Wales. It read:

I am his highness's dog at Kew;
Pray tell me, sir, whose dog are you? 

This is a very simple and clever example of a genre sometimes known as occasional verse. It does not have the profundity or complexity of "The Wasteland" or of Pope's own "An Essay on Man", but that is not its point.
Poems should be judged according to what they are trying to accomplish. A limerick succeeds or fails according to how funny it is and how well it serves to entertain its audience; complexity would get in the way of its success. Traditional epic should be judged not on complexity but on the way it vividly and memorably conveys cultural tradition. 
In lyric poetry, some authors excel in creating complex works that engage the intellect as well as the senses and have multiple layers of meaning. Much of modern poetry and metaphysical poetry follow this model. Other poets succeed by creating simple and beautifully crafted lyrics such as Housman's "Loveliest of Trees, the Cherry Now."
No one type of poetry in inherently superior, although when selecting poems to read in the university classroom, one should choose complex and difficult poems as they provide greater challenges for students.