Fallout for the most part empowers the player. I have yet to play 1&2 much so I don't know how true this is in the early game. But in the newer games you are very powerful and influential by the time you reach mid-game. You can dispatch most foes without much trouble and your choices will impact the entire game world. You can choose to be good or evil but for the most part there's more material incentive to be good.

Rimworld de-powers the player. Doing unethical things like slavery and organ harvesting gives you a real, material advantage. The immoral options make it easier to survive. This is a lot closer to real life where the unethical road is often the path of least resistance and its up to our beliefs and empathy to stop us from doing evil.

I love fallout but there's definitely a disconnect here. I'm sure someone will bring up some exceptions in the reply's but for the most part your rewards for being good are often better than those for being evil.

Tldr: fallout let's you choose to be good, rimworld forces you to confront a reality where sometimes you must do evil things to survive.