I think that this book was in some ways a "filler".
GRRM intended a 5 year gap originally, and so possibly (and obviously we're trying to second guess the author, here) there was never going to be as much going on in this one - especially minus the Dany, Jon, Tyrion chapters which are probably the characters with more to deal with at the moment.
Having said that, for me important things
did happen in this book, although they are truly just 'setting the stage', as it were, for the storm to break.
***SPOILERS***
The militarisation of the Faith is significant as it gives the religious orders real political power again.
The fall from grace of Cersei is important as she, arguably, was the driving force behind a lot of the events of the first 3 books (killing Robert and forcing her father into the field of battle to protect his grandson, perhaps before he was ready to do so)
The attack of the Iron Islanders against Highgarden may be a sideshow somewhat, but it's a sideshow which will impact on the powerbase at Kings Landing, as will the fate of Loras (what is it about the Kingsguard? Worse than King Tut's curse!
) and Margery.
Dorne was one of the biggest mysteries of the series so far;
Who's side are they on? Why didn't they support Kings Landing? What are they up too?
This book answered those questions and provided some new characters to watch out for.
Overall, I disagree that he has 'done a Jordan' so to speak.
He's broadened the scope of his series agreed, but he has not done so at the expense of the story - we needed to know what Dorne was up to, especially as it now looks as if they, or possibly the Iron Islanders, will play a key role in Dany's return to Westeros.