This is a lengthy statement but reading about everyones sortie frustrations lead me to this thought.
My personal issue really is that none of the primes outside of the horn are unique outside of their own associated weapon skills.
I don't dislike Sortie but I also don't particularly find it interesting/challenging. I have done it quite regularly up until the last few months or so but I enjoy being challenged in games. As masochistic as it may sound, I enjoy the process of failing over and over, trying new strategies and then finally clearing content. Odyssey did this well in my opinion and felt like a accomplishment climbing our way and eventually clearing v25.
Sortie unfortunately does not give me the same sense of accomplishment or desire to consistently do on a daily basis.
Now with that said if the weapons had unique traits/skills associated with them, I think the playerbase, including myself would be more inclined to grind sortie and in particular grind Aminon on a regular basis if the Stage 5 provided some sort of job specific unique skill/trait/spell etc.
Imagine the gun at stage 5 gave a unique roll or even a third roll, club giving potency to entrust or even a huge boost to duration so that it could be up full time. Shield giving shield bash an attack down or evasion down effect. Great axe could have "enhanced breaks". They gave BRD a new song... so it could have been done.
Some of those ideas might be to powerful sure and could be different, but my point is that its a long hard monotonous grind for a stage 5 shiny that essentially is just a powered up relic weapon without any "real" uniqueness.
My thought process goes to the new master trials that to the best of my knowledge no one has cleared the recent two. Amongst other dilemmas in the fights, it's known that accuracy is an issue... lets say your stage 5 gun gives you a third roll... all of a sudden you can have chaos/sam/hunters and maybe then not having soul voice madrigals is such an issue.
That would make more sense to me as to how our new shiny primes could be useful in these so called Master Trials that are for "us to have somewhere to use them".
This just...isn't how Ultimate weapons work. With the exception of mythic weapons (the only Ultimate category which is job-specific), instruments (because what else could they do...?) and shields (kind of, but not really), very few of them actually change the job.
Relic: The only one of these that offers anything that changes the way you play the job, or adds any new functionality to any job are the gun/bow
Empyrean: None of these do absolutely anything that changes the way you play any of the jobs
Aeonics: None of these do absolutely anything that changes the way you play any of the jobs
Unless you consider "able to make new skillchains", which primes do, then none of the ultimate weapons do anything to change your job or how you play it.
I guess Su5s kinda count? So...there ya go I guess. Considering that Prime weapons have multiple jobs on them, I would not expect that they will ever, under any circumstance, include job-changing things like extra rolls.