To be fair, in the 70īs this was rather "new and different" music but in general i never felt ever that his music had a long term value.
My criticism was directed at his post 70s and current music. To me his 70s classics do have long term value. When I listen to Mirage or Moondawn (also a bit of 'X') from time to time, I am still almost as excited as when I heard it for the first time. There's something wonderful and organic about those discs, something he has never managed to capture again. (Some of KS' moments on the Dark Side of the Moog series are very good though.)
If we're going to compare with Steve Roach... well, SR has moved way beyond KS & TD territory with some of his music and I believe he is still moving forward one way or another. So in my opinion... KS & TD 70s classics stand firmly among the best electronic/ambient music of today. But SR has been more consistent in quality and more innovative over a longer period of time.