To be fair, one could make a similar critique, and more strongly, of Nietzsche.

Also, although I think the critique is correct of people who are moved primarily by arguments (one would hope most philosophers fall into that category, but...), it's less correct for those who take a more intuitive approach (which generally involves more emotional affinity). Evocative prose does move people to change their perspective, though in a way largely uncorrelated to the truth of the propositions (if "truth" is a coherent concept for that subject matter--usually yes, but if it's a poem about the joy of ice cream in summer, maybe not).

And of course there's always the possibility that one's prose isn't as evocative as one would like to believe. It's much easier to check whether one has a sound and valid argument than a moving style.

So I think the evaluation of "won't persuade" is stated a bit too strongly. The more telling critique would be: the degree to which it persuades is independent of its truth value. If one has the Voice of Saruman, it doesn't mean that Isengard has always been the friend of the Rohirrim; it only means that the unwary or weak of will can be led to think so.

But I agree with your overall sentiment. This is literature, and literature works to persuade; yet it does not substitute for an actual direct non-metaphorical argument.