Swift's prose is elegant and of its time. The issues that his satire relates are also, sadly, grounded in their time and lose some of their punch regarding political statements. There is a reason we know "A Modest Proposal" more than we know about "The Battle of the Books" or "A Tale of the Tub."
A better way to say this, Swift is at his best when his writing follows his name and the length is commiserate to the argument.