Almost all statements here are either incorrect, disingenuous or an exaggeration.

1. It took him 30, not 40 years to publish the last book, counting from the first (82 to '12)

2. The last book is an extra. The series effectively ended in 2004. So that makes it 22 years since the first.

3. The books were published with an average of 5 years between each, so it's not like the last ASoIaF book, almost twenty years on the making.

Which is to say, no, the Dark Tower should no be used as reference for this kind of comparison :)