That WHM itemization reasoning <3
"Hey let's assume I'm always chaincasting and never interrupt any cast, spell speed is the best stat".
Haste always is, and always has been the worst stat for healers, unless either:
A. It scales significantly better than other secondary stats
B. It scales better than simply more haste = most spell casts (For example with haste providing extra/faster hot ticks)
C. Mana is a non-issue (And even then, you'd usually weave in more time efficient spells at the expanse of mana efficiency, instead of chaincasting low efficiency spells)
Edit for clarity : none of the above are valid for FF14