Conversations like this are really fun!
I think a whole lot, and I ask questions a lot too. Please don't mind me if I get wordy, I know I can be quite the long winded airbag but I get so passionate about wondering of how things work and how they are done and why's and what's and when's and etc lol...
I always liked to think that because Sailor Moon is a brand new Sailor Senshi, she has tools that are meant to hone in on her power and magic, and focus it since she can't exactly control it herself.
I feel this is where the transformation item comes from, as well as all other senshi artifacts like tiaras, wands and etc.
Some senshi are new, so they need an item to focus and direct that attack, otherwise it will let loose and could hurt anyone around them severely and not just the enemy.
Like many other shows, power and magic are most often depicted being utilized by the emotions somehow to strengthen an attack or defense.
I feel like Sailor Moon has so many items, because she is so new, and that because of that, she needs the extra help that others don't have.
But then there is the case all senshi have a transformational item(senshi crystal storage device and senshi crystal) and some having tiaras and even a few having staffs/swords/talismans of sorts.
How can I explain that while sticking to this theory?
Well, I imagine some weapons like that of Sailor Pluto in the manga, were gifted items that are inherently magical on their own without a user. This includes all Sailor Senshi Star Seeds the Sailor Crystals/Senshi Crystals. This works because her Staff's main purpose is a key that controls the Gates of Space and Time. The gates, and the duty of watching the door was given to her to guard by Queen Serenity.
But she uses it in her other attacks? Every Attack aside from her Pluto Dead Scream is a power directly linked to the gates. The rest of her attacks MATCH her godly namesake, that being of death/souls/underworld.
But what about her Talisman at the top of the staff being her pure heart? That was anime continuity only. In the manga, Queen Serenity gave Pluto the staff and Garnet Orb, Uranus the Space Sword, and Neptune the Deep Aqua Mirror. (I have amazing head cannons for these items and purposes and powers fyi)
This proves that her attacks such as opening and closing the doors and transporting to the gates, Time Stop and Dark Dome Close(A move she uses to close any doors not just time doors as seen when she closed the dimensional doorway in the Infinity Arc) or that acts as a warning of the awakening of Sailor Saturn. The Garnet Orb also acts like a visual aid as seen in the early pages where Pluto shows them the face of the enemy. Both Garnet Ball move being a shield and Chronos Typhoon energy cyclone attack are done without the staff key and only the Garnet Orb.
The three talismans in the manga are also said to be combined in order summon or recognize the awakening of Sailor Saturn but they also resonated with Sailor Moon after she, with the support of Mamoru and Chibiusa, "Created" the Moon Chalice.
Why do I say created in quotation marks? I'm getting there
SO the point of all this? SOMEONE created these items, to either surpress magic from wildly exploding everywhere, releasing magic like in order to transform, and to focus energy at a direct target.
Sailor Saturn's Glaive was not given to her by Queen Serenity that we know of but like I said before, it could have been made still just to help her control and channel her powers so that those around her aren't unintentionally hurt during any emotional outbursts. That accidents that could happen are frightening! Especially considering her kind of power.
Sailor Moon's first real weapon is a tiara. During her emotional outburst, I imagine the orbs and broach and etc were meant to channel that magic but her power is so vast that it could not contain it and thus everyone, not just the enemy was effected by an uncontrolled release of power because the amount of power she has was unmeasurable. Hence, the source of her power, the silver crystal, these most powerful crystal in existence.
(While it can be said as a continuity error between arcs that Usagi "Inherited" the crystal during the first arc but later arcs revealed it to her be sailor crystal(Source of her soul, without she will die/can't be reborn into a physical body) it can be said that Queen Serenity was holding onto it until she could handle it herself or was in training of sorts. I've seen many people use this theory and variations of it.
This works because Sailor Moon practices the use of the moon wand, almost preparing her for when the crystal sits inside it and she can really use it to attack more powerfully, and focus the energy of her power in a specific direction.
(Likewise, a what if theory on the basis of combining continuities of manga and anime, Chibiusa's beam of energy messes with gravity by making things lighter, while Sailor Moon's sonic booms could be said as a means of making air pressure, or even gravity heavy enough to damage.)
So I feel as if her Tiara, orbs in her hair and other items(even fuku costumes. Why are they similar? They are a military uniform, that's why. Who is to say they needed to transform in order to use their powers in a past life? Perhaps the uniforms are meant to showcase status while also fashionably decorating their outfits with practical magical items that strengthen and/or repress and focus and release energy.(Another example of this? Sailor Jupiter's Lightening Rod. Sailor Moon's tiara is not the only one with multiple functions.)
Speaking of Tiara's, the stones are different colors. Taking in Naoko's line of work and hobbies... gems and stones all have mystical meanings and properties.
Maybe the Tiara's are power gems.
"
The ancients associated Emerald with the Greek goddess Venus, the goddess of love and beauty, it and was said to protect lovers from unfaithfulness. If the heart was loyal, the gem would glow in a beautiful green color, but if the heart was went astray, it would turn a different, lifeless color. In addition, it was believed that wearing an Emerald would improve one’s memory and intelligence, enabling one to think clearly about the past, present, and future."source
I imagine Jupiters gem is an emerald. As we have seen, Makoto is prone to heartbreak. In her story, The Melancholy of Makoto shows she is prone to forgetfulness and she struggles with studies from time to time because she is easily distracted and needs help with clarity.
This could be the same for all gems because they don't have to match their birthstones but their needs.
Just my thoughts