Pretty Guardian Sailor Moon/WMG

Sailor Moon was never meant to be a real Senshi.
She was meant to be a strategic weapon.

Compare the differences in power levels between the planetary senshi and Sailor Moon. The senshi are tactical, fighting essentially on the unit level. Moon is capable of devastating entire planets. Without direct In-Universe evidence, it can't be known for sure; but it's likely that the senshi were empowered in some way. Moon must have been similarly "manufactured".
 * Interestingly, older continuities promote this idea, but for different reasons. In the manga, Sailor Venus is usually supposed to be the true leader. In the anime, the Sailor Moon persona is a new anomaly born from Princess Serenity's desire to protect her friends. This is supported by the appearance of the Moonlight Knight, who was subconsciously created by Endymion in the filler, and by no one even suspecting that Usagi is the Princess initially.
 * This is not that far from Sailorsaturn's role in the anime and manga, so the idea has existed in the series before.

The "Terminator Moon" personality who shows up at the end of the series is Sailor Moon's real, original personality.
"Princess Serenity" was an artificial persona applied over it to make dealing with the weapon easier or to camouflage it.

Usagi is a real persona who grew up around the weapon identity, probably unintentionally, as a side effect of the reincarnation.
 * It seems that the "Terminator Moon" effect was first created by Serenity's personality getting overwhelmed by the Silver Crystal/Metaria when Endymion died. Since Serenity is still an open conduit for the Metaria, whenever her personality manifests in Usagi, things tend to start quickly going boom around her.

If Sailor Saturn exists in this continuity, she will have a different power set than that possessed by the anime/manga version.
Because "Terminator Moon" already has the "world-killer" ability.
 * Well, considering Terminator Moon's got Saturn's powers, it'd make sense that Saturn has the original Sailor Moon's powers -- namely, to heal and to bring people back to life.
 * Sailor Saturn/Hotaru had healing powers in both the anime and manga, so it's not much of a stretch.

"Princess" Sailor Moon is a reincarnation of the Ide energy taking its third swipe at Human existence
Princess Sailor Moon is even jokingly referred to as "Sailor Ideon" in some circles.

In short, the Ide in Ideon sought the destruction of both humanity and the Buff Clan because it viewed them unworthy of existing. It destroyed everything but wasn't able to stop everything being reborn.

Cue "God gigantis: Ideon vs Gundam" where Amuro and the ZZ protagonist have to deactivate the Ideon before Neo Zeon can do anything stupid with it. Swing and a miss for the Ide.

Though Humanity does itself in several times (End of Clasic Gundam some time after V, G Gundam, Wing, X, Seed and Turn A - 00 happened prior to Ideon), it always comes back. Turn A's Moonlight butterfly technology turns all techonolgy to sand and ends the Gundam meme permanently.

In the Silver Millenium, the Ide is reborn as Princess Serenity and, forgetting itself, falls in love with Endymion. The war between the Earth and the Moon happens, and Endymion is killed. The Ide reawakens and destroys everything in a fit of madness before killing itself, and it is then reincarnated into Usagi. This leads us to the events of PGSM.

As for Saturn, instead of being the Ide (which strives for non-existence), she is the force that strives for the cycle of birth and death. Her powers will come from the necessity for there to be an end in order for there to be a beginning.
 * So Saturn's the Dis Lev?
 * This could mean that Queen Beryl is Irui Gan Eden.

In this continuity, the Four Generals are the outer planets' guardians.
Jadeite is Uranus's, Nephrite is Neptune's, Zoicite is Pluto's, and Kunzite is Saturn's. It explains how they were so different from each other and more powerful than their other versions.
 * In this continuity, they might be the counterparts of the senshi, with each male/female pair representing a planet. They're equal to the senshi in power. If Mamoru is still the host of the Golden Crystal, it makes sense that they are to him what the senshi are to Usagi. Word of God says there are no male senshi, but we already saw senshi with male civilian IDs in the Sailor Stars season of the Sailor Moon anime. This is another Alternate Continuity, so we can't rule this theory out.

Pretty Guardian Sailor Moon actually has the Dark Kingdom's plot, but Sailor Moon S's ending.
There's no denying the main plot was centered around the first story arc of the manga, the Dark Kingdom, but the climax and ending it so obviously based almost directly on Sailor Moon S, and the Senshi of Destruction and Rebirth. . . only instead of this Senshi being Sailor Saturn, its written as Sailor Moon instead. Both Usagi and Hotaru are innocent girls faced with fate, both have the power to destroy the planet, both have a horrible entity they can't control inside of them (Princess Serenity and Mistress 9) and both end up dying only to release the power of "Rebirth" in the end. Obviously the writers didn't like the ending of the original story but enjoyed the higher stakes and drama of the Sailor Moon S arc, thus, this is a retelling of both plots meshed together into one.

"Terminator Moon" is a combination between Sailors Moon and Saturn.
Saturn was Princess Serenity's best friend in her past life. When Saturn took a hit for her friends, Moon absorbed Saturn into her body to keep her 'alive' in a sense. This caused Serenity to possess the power to destroy worlds, as well as causing her to act stronger when it comes to things she loves, namely Endymion. This led to the plot of PGSM.