We see quite a few otherwise quite good representations of livery shafts with widely spaced whipping on the fletch.
And these usually have one other thing in common, which is the barbs forced apart in some degree by the angle of the thread.
Clearly, too thick a thread will always force the barbs apart, but a lot of folks seem to overlook the correct and the cleanest method of whipping on a fletch and why it is functionally the better method.
By employing a suitable number of turns to the inch, the thread will run more nearly perpendicular to the fletch and so not force apart the adjacent barbs.
Ask yourself why this should matter, shooting a heavy shaft for distance.
Clean or not? That it was a little more work to create a clean fletch does not appear to have been an issue with the mediaeval fletchers.
And then there is the matter of coating the shaftment, reasons for embedding the thread.