Lee, thank you so much for this excellent demonstration on the topic of the early use of threaded tangs !
Also for the wonderful photos from Drummond
a book I always dreamed of having!
If I may just add an unrelated note on that illustration, the hilts in the uppermost left and lower left of the six shown are actually Italian schiavona not Scottish.
In the time of Drummond's work it had been presumed that the Scottish basket hilt had either derived from the schiavona or been closely related. It was later of course shown that the two hilt firms were structurally different and in fact not related as seen in the 'lattice' type character of the schiavona .
The question on the pragmatism of the threaded tang adding to the strength of the blade attachment in combat seems well placed. In fact the Scottish two handed sword known as the claymore (my Gaelic is rusty, =great sword) was a huge two hand sword, and as the blades on these were often cut down to use in basket hilts, the term often was used in describing them as well.
While by far, not one of the 'experts' , the use of the threaded tang seems more a convenience for field repairs or replacement blade......but the added strength seems most reasonable as a purpose.
The hilt on this example shown dismantled is indeed English as used by dragoons in units of English cavalry through 18th c. but was probably produced in the 'garrison' context by hilt makers in Scotland.