The Sailor Guardians of Sailor Moon are among the most absurdly powerful teams in anime history... but their power levels are nothing compared to their manga counterparts. The Guardians in the manga can warp reality, obliterate planets and even rewrite the laws of reality itself! The original anime failed to really convey the sheer level of magical power inherent in each Sailor Guardian.
The Four Forms of Sailor Senshi
In the '90s Sailor Moon anime, Usagi achieves three core transformations: her standard Sailor Moon form, Super Sailor Moon and Eternal Sailor Moon. The other Senshi reach their Super Forms but go no further. Each transformation is triggered by some exterior magical force, and each form grants the transformed Sailor Guardian even more power.
In the manga, every Sailor Guardian gains an Eternal form. This grants them power comparable to Eternal Sailor Moon. The Sailor Guardians also have Princess Forms, present in the manga but not in the original anime. These forms are stronger than their Super forms but weaker than their Eternal forms. To understand the power of the Eternal Sailor form, remember that after transforming into Eternal Sailor Moon, Usagi obliterated Nehellenia's Mirror Dimension -- destroying an entire universe. The other Sailor Senshi gain comparable power when they gain Eternal forms.
On top of raw power, the Sailor Guardians are capable of traveling across the universe in seconds, enduring the gravitational force of Black Holes when right near them and trading blows with the corrupted Sailor Guardians of Sailor Galaxia, all of whom are capable of obliterating worlds themselves.
Every Sailor Senshi gains immense raw power of their element by the time the manga comes to a close and they fight the forces of Sailor Galaxia -- though, of course, Sailor Moon is far stronger than the rest.
All of the above discussion ignores the sheer magical power of Sailor Cosmos, Usagi's future incarnation capable of combating the inter-dimensional personification of all evil in the universe. She, along with Usagi and Sailor Galaxia, are both capable of eradicating the entire universe itself at the end of the manga, though Usagi stops Galaxia and persuades Cosmos not to.
Sailor Cosmos can travel through time, rewrite physical reality. She is, in essence, a literal God. She also never appears in the original anime, with her Chibi-Chibi form being reinterpreted as Sailor Galaxia's spirit, cast off from her body.
Why Does the Anime Tone Them Down?
While Sailor Moon Crystal and the upcoming Sailor Moon Eternal movie adapt the manga more faithfully, the original anime brought the hijinks down to a more human level. In order to maintain the threats of the monster-of-the-day formula, the Sailor Guardians would be overwhelmed by common enemies with sometimes gimmicky attacks. If the Sailor Guardians could just blow up the planet to eradicate every monster-of-the-day, it would make for a far less entertaining story.
The '90s series' most extreme show of Usagi's raw power is when she pursues Sailor Saturn through a dimensional portal during the fight with the Lovecraftian entity Pharaoh 90. Usagi pursues Saturn to save her from her own attack, as Saturn has the ability to bring death to anyone at the cost of her own life. Usagi returns with Sailor Saturn as a baby. It is uncertain if Usagi had to endure the raw death force or blow up Pharaoh 90's cosmic horror mass. Regardless, when the other Sailor Guardians gain Super Forms, they gain power comparable to Usagi's in that instance.
Even in the anime, Sailor Moon can blow up a planet with the Silver Crystal by the end of the first season. She just chooses not to because that would mean harming those she loves. However, when faced with Death Phantom, a literal sentient planet at the end of the second manga arc, Usagi demonstrates her full planet-destroying abilities. It is probable that the other Sailor Guardians in the anime have comparable power but never find a chance to truly demonstrate it.
The manga not only adds powers but it also gives the Sailor Guardians more time to demonstrate their full destructive strength in their fight against evil. The Sailor Guardians are strong enough to destroy universes before even reaching their final forms. The boys from Dragon Ball Z wish they were this absurdly powerful.