Trademarking titles from merchandising has gotten out of hand. The result is in my opinion beginning to eat into the fabric of poetic expression. I see the need to prevent pirate from stamping out unlicensed copies of books and paraphernalia, but I'd like to see criminal penalties for commercial plagiarism displace the use of trademarks in literature and entertainment.
I can see why "Wheel of Time" need to be a brand, but trademarking the words means that another author who has a completely different take on the term is prevented from doing much with it without awkward constructions. It's an old argument though.
Upshot is that the names of the individual volumes don't really need to be all that unique as long as they are fitting. And frankly, I believe most people are concerned more with the series title and volume number. A gathering storm fits the tone of the other volumes.
The problem I might have with it is the issue of passivity. Rigney's titles follow a pattern that describes the beginning, plateau, climax and if it had ended with AMOL falling off point. The book titles help you know where you are in the concise novel The Wheel of Time. A Gathering Storm has less punch than Knife of Dreams where it should have had more and lead seamlessly into Tarmon Gaiden, a good title.