The problem with UE4 currently is that it’s quite cryptic to determine if the outside environment is sampled using importance sampling or not. If you have SkyLight present, but ray traced shadows on it disabled, but GI enabled, I am not sure if GI uses importance sampling when sampling environment or not. Anyway, to be on the safe side, you should generally first use ray traced skylight to make sure you direct lighting from your environment is right, and once that is verified, add GI for secondary bounces.
HOWEVER:
It is true that currently, ray tracing performance is still not good enough on current gen hardware to get accurate enough skylight direct illumination with reasonable performance for interior spaces. Sampling exterior environment from inside of a room with relatively small windows is still very expensive. That’s why we still have to fake it by placing invisible area lights into window opening. It’s a direct throwback to ancient late 2000’s / early 2010’s workflows. Ugly workflows where you have to manually eyeball color and intensity of your area lights to at least roughly resemble exterior illumination, otherwise you may get a brutal mismatch between interior and exterior exposure, resulting in often very unrealistic results of exterior environment being drastically underexposed compared to interior illumination.
In offline rendering, during the times when environment light sampling optimizations weren’t as advanced but requirements for realism and accuracy were already pretty high, this issue was solved by “portal lights”, which were usually a mode of area lights, which used direct area light sampling to project environment illumination from the outside. This still required you to manually place some sort of helpers or geometry inside the window openings, but it did not require the annoying step of trying to manually match the exterior illumination color and intensity on your invisible area lights.
I’ve posted it as a feature request, but of course, everyone ignored it 
https://forums.unrealengine.com/unre…or-ray-tracing