Flytier is right about the recipe for the Sol Duc Spey as tied by Syd Glasso.
On the other hand, when does a fly cease to be faithful to the original? I believe Glasso tied on Partridge low water hooks. Is it not a Sol Duc Spey if tied on a Bartleet or an Alec Jackson? What if you use synthetic floss instead of silk, or a seal substitute? Mylar tinsel? And you'd best split your silk floss to form a dubbing loop for the seal.
My reaction when I first saw Flytier's response was that it came across -- intentionally or not -- as dismissive of the very nice work Thomas does. Another approach would have been to say something like "Nice flies, PastorD. I notice you used teal for the throat on the Sol Duc Spey. Glasso's pattern called for black hackle, and I really liked the progression from light flies to dark that he established. I don't think the teal works as well in that regard as the original black."
Thomas is a wonderful fly tier. I admire his work and am always happy to see it. I hope that he's not discouraged from coming back to this forum.
Conversely, I've learned a lot from Flytier's postings, and value both the information and the feedback he's provided to me.