I find it extremely hard to believe that you literally cannot develop your game based off a couple lighting performance issues. There are countless ways to optimize, fake, or work around issues that present themselves. Start digging into some of the GDC presentations for the games of Horizon Zero Dawn, Star Wars Battlefront, Ghost Recon Wildlands, and look at what they encountered and how they got around them.
Coming onto the board and just creating a flame post about how horrible you think the engine is wont help you. Why not provide specific examples of what your working on and scenes where you are encountering issues so we can help you work them out?