Also, I think to a certain extent there has been a changing of the guard, so to speak.
MJ's Malt Whisky Companion has been around for a long time now, and the book was such an authorative work that for years he was simply regarded as king of the whisky writers.
However, it must also be acknowledged that the book didn't really have much in the way of competition. Sure, there were other books on whisky around, but none that provided tasting notes or scores so many different whiskies.
Jim Murray's Bible was the first book to compete and offer an alternative. Jim's timing was brilliant, because his book also picked up momentum at the time MJ's 5th edition of the Companion came out.
Many long-term whisky enthusiasts acknowledged that MJ's 5th edition did not do a good job of keeping up to date, at least with the tasting notes, i.e. he did not re-visit or update the listings from the 4th edition, he simply added in the new listings and repeated the old notes that were at least six years old.
This gave Jim a bit of an edge, and I think the title of "best whisky writer" has possibly shifted from MJ to JM as a result. It should also be acknowledged that MJ divides his passion with beer, whereas as JM is a little more single-minded.