There are some Earthbound references in Mother 3 that you won’t know the context of when you encounter them as well as a bit of context for the main villain. But other than that, it’s not required to go through Earthbound before playing Mother 3.
Yeah if I had to choose between Earthbound’s battling system and Mother 3’s, I would definitely go with Mother 3’s because the one for Earthbound isn’t as engaging.
I’m glad they decided to bring back this feature. Really missed having it.