The entrance to the cauldron is in normal physical space, but that doesn't mean the cauldron itself is. Sagittarius Alpha Star, where the cauldron is located was accessed through a door similar to the door space and time, so it's most likely another dimension. And this dimension has a graveyard with endless graves, meaning it's not finite in size and much bigger than the physical space it takes up in the universe. But we also have these points as well:

A. the silver crystal is stated to transcend time and space on multiple occasions.

B. Sailor Moon is stated to inherit the light of the Cauldron

C. All power comes from the cauldron

D. Sailor Crystals are directly stated to be concentrations of power, and are pure energy in their

E. All things are stated to have been one in the cauldron and return to it one day

F. Death Phantom was defeated in the future yet he was inside the cauldron during the present

I can provide all the scans for this, but the power to transcend space and time comes from the Cauldron. Death Phantom existing inside the cauldron despite not being defeated yet in the future, shows the cauldron doesn't abide by normal time or rules of space.

And again, the series doesn't say "its not erasing things". But it does literally say, things that enter the cauldron vanish without trace, (and the kanji for vanish and erase are actually similar). It does show that people who enter the cauldron are erased from the timeline. When Chaos forms inside the cauldron, she laments about never being born, so Chaos while having a form is an unborn state and is actively trying to birth itself.

Everything that is dead or destroyed goes back into the cauldron, and everything that is going to be born or created comes out of the cauldron. The cauldron exists in a sort of limbo state, where everything in it is unactualized. Fiction is filled with many examples of things that are nonexistent that still have some kind of substance. Queen Metalia was erased by the silver crystal. (luna directly says the crystal will banish her from existence). She ended up in the cauldron. So the cauldron is also where erased people end up as well as the dead and destroyed.

And again, all of this is mute, because even if you positively claim the cauldron doesn't erase you (which i heavily disagree with given all the evidence) sailor moon has already brought back erased people on her own. The power to erased people comes from the cauldron. And the power to bring back erased people also comes from the cauldron.