You’ll struggle to find anybody using World Composition and static lighting. I’m not entirely sure I follow what’s going on, but I will say this: Dynamic Shadows are okay and more than useable, even on a low-end device. We have two dynamic light sources on a mobile game for the entire scene, and the performance of those is the least of our worries.
If anything, in a large world your game will probably run considerably better using Dynamic Shadows because you won’t be streaming lightmaps in and out of memory all the time. It’s also much easier to manage in terms of lightmass building, which simply does not play nicely when you start using streaming levels and/or world composition. You can’t (without heavy workarounds) have different lighting styles for different streaming levels, it just doesn’t work - and you’ll eventually want an entire render farm to do lighting builds.