Larp is the main answer. No other game lets you larp as an actual evil empire. One that actively genocides undesirables.
Larper power explains it: but again, it's all so
clumsily done. Let's keep Sword of the Stars 1 as an example: the Zuul, a race of evil marsupials,
entirely works on slavery and stripmining planets and its economy is built on looting planets with specialized ships. Ah, everyone in the game gets genociding. Nuclear bombing. Bio bombing. USING MASS DRIVERS.
Have I told you that during the
fully simulated tactical battles in SoTS1 your
orbital bombardment ships are under your direct control and the UI has a fuckhuge button to let you fire when you want the death cannon? And it's a "light" 4x, with pre-done races and limited strategic overlay.
Stellaris has some very nice %s tho.
I'm not saying that Stellaris
theoretically does not allow such stuff, but it's all boring % and all in your brain, with almost no meaningful gameplay impact (you don't have to
get your slaver ships on planet and organize the raids!). it's pushing a button and the usual PARADOX PERCENTAGES change a bit.
It's like no one realizes there's a billion 4x that let you do the same. Just better and without PARADOX MARKETING POWER. Maybe it's merely that, marketing (people see Paradox and believe they know what they are doing).