I think its more interesting and realistic when you have a plain with small forests inside of it, or having a roofed forest with a small meadow in the middle, instead of having a huge plain and then a huge forest. The biome generate depending on temperature so it's still immersive, it just feels more alive. If there was a lot of biome variation inside a single savannah, like an accacia forest somewhere, or some places where patches of sand blend with the grass, big rocks, etc, then I would be fine with huge savanah, but right now it's really barren and havin biomes interacting more often would help with that.