Why would a "general mass of people" not want to prioritize a staff Empy? Well then here are the obvious reasons for you since you apparently like to ignore them then wonder why there are no reasons left.
1. It is a toy weapon with similar time/gil/effort investment to truly useful weapons.
2. It doesn't help LS runs to anywhere near the extent that a Kannagi, Ukon, or Verethragna do.
3. It doesn't increase the utility or potency of SMN to the extent that any other melee's empy does for that melee job.
4. I'm not even sure it increases the potency of SMN. Isn't SMN's calling card that they're largely out of AoE range and thus hate free, risk free damage?
5. If I haven't even seen an SMN in events for months, guess whether or not their empy is in demand.
If those reasons don't spell a clear picture to why it is a completionist piece and not a necessary piece, you're in denial about how Empys have effected FFXI, and how your LS really functions.
And before you respond AGAIN with "but it's their points, they can burn them how they want," just don't, because you're in denial over how useful a Hv{tab key} is, too. Alssuming that the "certain stage" reference is about taking that empy to 90, it is a complete waste of time as it doesn't improve the weapon's purpose, which is to recover MP through TP. The LS precedent, assuming that there is one about taking weapons to 90, is not that all weapons are taken to 90, but that Empys worth the effort to 85 are up for discussion about 90. If you thought that all weapons are taken to 90 carte blanche, you were wrong, because 90ing an Empy is no minor feat, and the time would be better spent 90ing something else, or starting another Empy.
Staff is not up for discussion because nobody gives a rat's ass about the SMN's staff's base damage or MP boost. I would find it offensive that someone would even deign to request my time on such a useless endeavor. I don't care what they do for me or the LS or anything else, if event time rolls around and it's time to 90 a staff, we had better be scraping the bottom of the barrel in terms of things that people want, because that is pretty damn low.
There are only so many hours in a day, and only so many of them do I wish to waste fulfilling some pipedream about melee SMN. I'd do it for a good friend to 85, but s/he better scratch my back right back.

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