The writing speed of Erikson is a bit overstated. The first three books took a bit longer than the rest to write, and Books 2 and 3 are widely regarded as the best in the series. Book 5, which is probably the next best-regarded one, also took a bit longer to write. It's the books that he had to fire off the most quickly, 4 and 6-8, which have become in for the heaviest criticism over their lack of proofing, editing or redrafting. Hence the timeline errors and purple prose.
Also, what a lot of people don't realise with GRRM is that the writing speed has not substantially changed. He wrote the first third of ACoK as part of AGoT before he realised the book was too huge, so he actually completed the published AGoT (which itself took over four years to write) well over a year before it came out, and as a result ACoK took about three years to write and AFFC closer to four (taking out the eighteen months he spent writing a different Book 4 and then scrapping it). So all of the books in the series to date with the sole exception of ASoS have taken 3-4 years each to write.
So the situation with ADWD is business as usual. The only difference is that lots of people obviously weren't as bothered about the situation with Book 1 and the author indicated at the end of Book 4 that the next one would be out more quickly. Well, unfortunately, that ship sailed a long time ago.
