Not a bad thought.

Ruby and Sapphire shed a bit more light into how Sugilite might have acted too. Ruby seemed a bit more like Amethyst in several ways, so it could be possible that when they fuse, Sapphire's personality takes more of a back seat, which is why she's so aggressive.

Though, the interesting thing to note is how Garnet thinks of her fusion, how she's "never alone" and a greater whole compared to them separate. Compare that to Stevannie, who felt more isolated and alone when they were together. It could be written off as the fact that they're new to fusion, or it could be something else. Might be something neat they could explore.