TWoK does start off slower than many books out there do.
It seems like it could almost be considered a standard fantasy trope in and of itself: the protagonists get introduced (if the work is particularly derivative, they will live in a nice rural village with happy, healthy peasants during a time of rejoicing), evil attacks, the protagonists have to flee, etc. Everything is very personal and very busy.
Then they start meeting kings, nobles and elves, we get a flipping ton of backstory, and the story broadens, spreads out, and begins to be more epic. It also tends to slow down. A lot.
Tolkien did it this way, of course; in his case, the only reason the story is remotely engaging before the Hobbits get to Rivendale is because of the sense of impending doom and the personal danger involved. Terry Brooks did it, as did Robert Jordan. It's a perfectly good way to start out an epic story.
In Brandon's case, though, he basically cut to the chase and started out with a broader scope rather than pretending it was one persons story. This does mean readers have to acclimate more to the abrupt start in worldbuilding rather than being eased into it. On the other hand, it also gives assurance that Brandon actually knows where his story is headed already. I don't mind reading an epic story if the author is honest about the scope in advance. I like this approach, as long as I know what I'm getting.