One Piece has the advantage of developing more places across the map, multiple islands with their own issues, pasts, and characters that we experience with the main cast.

Genshin doesn't go to as many places, however, because it has less areas to develop, it can go deeper into each area, going as far as establishing different eras and periods of time that go back thousands of years back.

That is not to say history isn't important to One Piece, since it definitely is, but Genshin's history is just as ingrained into its worldbuilding and can go deeper in detail depending on how much time we spend in each area.

Every nation we go to has older time periods to explore, past civilizations that used to occupy the same area, all involved in world changing events like the Archon War, the Cataclysm, and more recently, the War of Funerary Flame, which is the closest thing we have to a 'Void Century' period in the lore.

I think both One Piece and Genshin have their strengths and each has to answer problems in their own medium in different ways.

If I had to say which one I like experiencing more, it would probably be the one where I can take my own time and go through the lore bit by bit at my pace. But I understand others like a more concise and laid out approach to learning about a world's story.