It makes sense for Pearls as more of a status symbol. In real life, may slaves and servants of very rich social people in many cultures were treated very well (for the most part) and cleaned up nicely, because it reflected well on their owners.

And it does seem like Gems are made for specific purposes. Jaspers are heavy militarized, probably high-ranking given their strength, while Amethyst seems more like a grunt. While Peridot of course talks about how she was specifically made to be an engineer and technician, which also explains her limb-enhancers and how they manipulate their technology. And for Garnet, my guess is Sapphire is a much higher-quality gem compared to Ruby, considering her dress and the fact that she's very "princess-like".

Of course, it also explains Pearl's own personality. She's very clean and orderly, to the point of being very anal about it. Everything has to be perfect for her. Much like it would be to an obedient servant. And as we could already guess, she trained herself to use swords both to mirror Rose and as a means of "doing it for her".

As for Earth as a whole, I think Homeworld is essentially just an Empire. They come to other planets and take over, using what resources they want while probably enslaving the inhabiting race. Pearl herself specifically says they fought for Earths "Independence".

This supports my head-canon of their being multiples of the same gems, not just pearls but every gem. The number of them is determined by their rarity in real life, for example Diamonds are rare, and colored diamonds are rarer so it makes sense there is only one Yellow Diamond. This could also explain why Garnet left Homeworld, Rubies and Sapphires are pretty rare gems, but Garnets are not as rare. Thus their fusion would be looked down on for being of a lower class. I only hope that this multiple gem thing doesn't result in an army of identical clones, but instead a variety of different shapes, sizes and personalities of the same gems.