Does this hypothetical also exclude Tuxedo Mask as an ally to Sailor Moon along with all the other Sailor Senshi? If it does, then that would greatly affect the series as a whole since, not only would this hypothetical make the series no longer a superhero team series, but would also eliminate the romance genre that it's also a part of. Part of Sailor Moon's creation was not only its being part of the superhero team genre that Super Sentai is a part of, but also its being a romance series. Remove both the remaining female hero teammates
and the male hero ally and you end up with a completely different series that is twice as removed from the version we ended up getting.
Moreover, the removal of Tuxedo Mask (and by extension Prince Endymion) also removes (or at least severely alters) the Silver Millennium background and all the present day stuff related to it. Queen Beryl's backstory no longer bases itself in her jealousy of Princess Serenity catching Prince Endymion's affections, thereby altering Beryl's original motives as well. Endymion and Serenity also wouldn't have the same tragic deaths that they had in the real version, meaning Queen Serenity wouldn't be spurred by her grief into using the Silver Crystal to seal away the Dark Kingdom and send all the good guys to reborn in the 20th Century, at least, not in the same way as she was in the real version. And as Tuxedo Mask wouldn't be around to take a lethal blow for Sailor Moon in the present day, her grief for his injuries wouldn't spur her to cry the Silver Crystal out of one of her tears. What's more is that the whole ordeal with Crystal Tokyo wouldn't be the same either, as Chibusa herself would have to be gone too since she becomes another hero teammate, thereby significantly altering the story of the Black Moon clan.
And for all the others to gone, there'd be no Sailor Pluto to aid in the time traveling stuff, no Uranus and Neptune to drive the Death Busters story forward, no Sailor Saturn to befriend and help bring the same resolution to the Death Busters story, and no Sailor Star Lights to help drive the plot of the Shadow Galactica story. In fact, there's be no Sailor Galaxia or any Shadow Galactica Sailor Senshi either since Sailor Moon would be the only Sailor Senshi there is, meaning the very concept of Sailor Senshi wouldn't apply to anyone but her, nullifying the whole "Sailor Senshi from all over the galaxy" concept in and of itself.
In short, putting Sailor Moon by herself as the sole starring hero of the series would have quite the repercussions on the series itself as we know it when we start to think about it more.