Theory: Lapis is Supposed to be a War Gem/ A Minor Talk on Homeworld Class

Now we don't know what brought on the nobility status of Lapis, but we can guess. I think that any and all gems can acquire this rank, but only when they become harder to find. When gems stop being able to be brought out of the dirt, they become increasingly rare, and their value goes up, just like our real worlds gems!

(Except diamonds, because those aren't as rare as you'd think)

Now there's a few set backs to Lapis' being designed for war. One of those is going to be their durability. From what we've seen, a single punch from Bismuth is enough to poof this gem.

Lapis is a high attack, low defense gem and may have been trying to fight along side the Jasper's in the scene, until they began losing and she had tried to flee. Speaking of which....

FUSION!!!!!!! Lapis' may have originally been thought of to help Jasper's by fusing with them!!! We all know of the juggernaut known as Malachite, and that's exactly what she was meant to be. A massive monster that can fly, control water, and is now a tank beyond belief. If Jasper can handle two direct explosions, a fall at maximum velocity, and have a ship fall on her, then Malachite can handle more. Think of the gem placement on Malachite.

Tactically perfect for war. The nose and the back. The back is genius, but the nose is odd, well unless you add in the helmet. Yes, now they have protection over their vitals and can practically fight freely without worry like Garnet. Then manipulating water is a massive upgrade. Jasper, like all quartz's in the show, provide massive upgrades to fusion. Malachite had a very easy time summoning water up and around and manhandling Alexandrite.

Controlling/manipulating water comes in handy when contending with opposing organic life. At the very least, the majority of our planets creatures have water inside of them or need to drink it. Lapis, by herself took an ocean to space by forming a pillar.

she also had no problem parting the water. Malachite may be able to do much worse and manipulate more bodies of water at once, or even go the "avatar: the last air bender" route and blood bend. This means that she can force creatures to do what she wants by manipulating the water in their bodies. Given more time as Malachite, to learn and grow, this may have happened. It's a good thing Steven didn't fuse with everyone. Being able to freeze water instantly would ruin any ecosystem on the planet. Even comets and astroids have Ice on them meaning malachite could potentially pull one to whatever planet she's on.

She is a literal apocalypse waiting to happen. So why doesn't homeworld use this!? Oh that's right...FEAR!!!!! Homeworld has to know something about the potential of fusion that they possess and could've stopped production on lapis for this reason. There became a rarity because they had to stop making such a dangerous gem. The only relative to lapis is sapphire, who does not control her powers in the way or on the scale that lapis has. Sapphire should be feared more, due to future vision, but isn't. Probably because she doesn't have the same damage potential. The diamonds literally couldn't stop such a gem. Lapis was able to render Garnet useless for a few moments while she made her escape, so Malachite could easily do this to diamonds and be able to physically contend with or be close to in power with one.

So they try to hide it by giving them a high status and shrug off their need for war. They don't want something so terrifying going against them.