If you asked Dante or Spenser, or any other poet before 1800, whether it was more important to write good poetry or to put across a certain message, you would be met with incomprehension-- the question itself would not make sense. I think the whole dichotomy is the product of the late 19th century, and has done immeasurable damage. Even to my own thinking, at times.
There's an insidious logic here that the worse a poem is, the more effective it is at communication. We are given a choice between aesthetics and politics. The political advocates are worse formalists than the pure formalists, because they use poetic crappiness as a badge of honor. The formalists / aestheticists, on the other hand, have an allergy to only one kind of subject matter, the political. Political poems worked fine before, somehow, but at a certain point they stopped working.
There are a series of reactions and counter-reactions. It is all very mysterious and I haven't figured out yet how it works.