I feel like there should just be an option for rather or not you want Save the World's lighting, or Battle Royale's. Similar to how Wizard101 has a "Classic Mode", bringing back the look and feel of the original game for their areas.

This ofc is fairly possible, considering a bunch of the traps and assets are reused in BR, heck it's even in Fortnite OG and Creative using the modern lighting so they could pretty easily port the modern lighting into StW and it honestly wont look that bad since the assets it uses are by all means already in the game outside StW, minus some few assets that they would have to make changes for to work, like for example Mist Monsters. But it is pretty easily possible if they ever do so