Currently, the meta for Stellaris is focused on hard power (aka military might) that forces most if not all empire types to become OP through conquest. Early to mid-game is conquesting as much as possible until you steamroll into becoming a superpower as there is a positive feedback loop (conquest > access to more resources > strengthen military + maintain or increase stability with more resources which repeats step 2 > repeat).
It doesn't help that this playstyle becomes even more OP with DLCs included (Juggernauts, Mega shipyards, Titans, Galactic community decisions increasing soft power through military power).
To allow other playstyles to become optimal, I suggest overhauling the faction system to react and influence the player's actions.
Currently, the factions system doesn't do much to affect your empire apart from making political power, affecting happiness which affects productivity (which can easily be counteracted if you create above 20 amenities on a planet), and changing ethics. I propose that the system should be overhauled to allow factions to have a larger impact on happiness, stability, ethics attraction, and crime. In addition, small events benefitting or harming the player.
Ideally, this overhauled factions system allows a tall playstyle or pacificist empire to be efficient by appeasing its factions; increasing stability, happiness, empire ethics attraction, and lowering crime. This would cause a positive feedback loop, enhanced with small events that benefit the player once a certain threshold has passed (eg High stability on the planet attracts businesses, increasing trade value temporarily).
In contrast, an expansionist or aggressive empire would become inefficient. By rapidly conquering neighbors you integrate pops with differing ethics and/or species, empowering other factions or angering your main factions: decreasing stability, happiness, empire ethics attraction, and increasing crime. This would force the player two options: adopt more extreme measures (slavery, extermination, enforcers etc) to continue conquering or allow the empire to readjust before continuing their conquest, giving pacifist or tall playstyle empires more breathing room. There would be small negative events that would trigger once a threshold was passed (eg low happiness on pops with slaves creates movement for the abolishment of slavery, xenophilia/egalitarianism attraction increases temporarily).
This is as far as my suggestion would go though as any more additions would fall outside the scope of this post.
More about StellarisPost: "Nerf military power in the game and diversify playstyles by overhauling factions to influence the actions of the player" specifically for the game Stellaris. Other useful information about this game:
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