The problem is the way surface lighting/scattering is calculated, which does not match what traditional offline renders do.
My issue with UE is the opposite, the engine went too far into cinema production, and making it a performant game engine requires code refactoring. At which point an open-source engine might be a better choice. Its a mix of two (three) worlds, and not the best choice for one specific use.
For what is actually hard to do, like character animation, UE is a good choice. The lighting can be replaced more easily than the animation system.
My issue with UE is the opposite, the engine went too far into cinema production, and making it a performant game engine requires code refactoring. At which point an open-source engine might be a better choice. Its a mix of two (three) worlds, and not the best choice for one specific use.
For what is actually hard to do, like character animation, UE is a good choice. The lighting can be replaced more easily than the animation system.