Meursault:
In an earlier post you said: "Firstly, I think that the puzzle is fundamentally flawed if it cannot be progressively solved, instead requiring a big bang." This is demonstrably wrong as follows from this rule for Playfairs:
If plaintext ab encodes to cd and c and d are in the same row (or column), then a and a are also in that row (or column) and a directly precedes c and b directly precedes d.
No 'big bang' is needed; one does need to cold solve clues 23a, 29a, 33a, 41a, 12d and 35d (or enough of them to make progress, but most of those are fairly easy by Listener standards. If you do that, you immediately have 48% of the Playfair without any other solving needed:
P A _ _ I
_ G B O _
_ _ _ F_
L _ _ R T
_ _ W Y _
which forces:
P A _ _ I
_ G B O _
_ _ _ F_
L _ _ R T
U V W Y Z (and tells you both S and X are in the keyphrase)
That is clearly enough to discover the keyphrase.
Just because you (apparently) failed to find the logical entry into this fine deductive puzzle, you concluded that it must be “fundamentally flawed” and apparently felt the desire to revenge yourself on the setter, Horvendile, by blurting out the answer even though no one had asked and in fact others asked that you not do so. How arrogant you are. Why not just post the entire solution? That’s the logical corollary to your spoilsport attitude.