Yeah, grass can help in both directions. My long haired cat likes to have constant access to grass, it actually makes her puke less. My guess would be that the fiber helps to break up the hair clumps and move them faster down the digestive tract. But I’ve also had cats who only ate grass to make themselves puke.
Probably depends on the individual cat.
The last one sounds like Mushoku Tensei/ Jobless Reincarnation