Is he? he's taking 7 years to write a book, D&D have months to write out 1 season. Book 5&6 were so freaking slow and boring compared to books 1,2 and 3. So if it takes Martin 7 years to get out of the mess he has put him self into can you really blame D&D if they're having some issues getting out of that mess when they only have a few months?
Everyone is entitled to their opinion. I think books 4 and 5 (I'm pretty sure that is what you meant) were strong. I would have agreed with you after reading the 4th book, but 4 and 5 were supposed to take place at the same time, and he basically followed certain characters in 4 and other characters in 5. I thought 5 was a very good read, and appreciated 4 much more after I finished 5.
As to him taking so long to write the 6th book, I agree that it is ridiculous. But, I have a few counterpoints...
1). I think he could have cranked it out much sooner, but doesn't want to sacrifice quality for speed. If true, I guess I can somewhat understand.
2). I wonder if part of the delay is due to him wanting to take the story in a different direction than GOT has gone. Maybe he had a plan, but has scrapped a lot of it and is somewhat starting from scratch.
3). I think this might be a big one. Published books can only be so many pages. Let's assume that he finished WOW 1 year ago and had a manuscript that was ready to go to the publisher. At that point, he has to give consideration to Book 7. He has a bunch of loose ends that need to be tied up to conclude the story. He has 3 options.
A). start writing Book 7. If he can't fit everything into 1 book, announce that there is going to be a Book 8.
B). Plan to write Book 7 and tie everything up even if Book 7 sucks due to him cramming too much story into too few pages.
C). Outline/Summarize every chapter of Book 7, and go back and revise Book 6 if he feels that he can't possibly tie everything up in Book 7. Kill off some characters earlier. Combine characters paths sooner, etc.