The default brightness for the SunSky actor is 75000 lux. You can prevent it from looking washed out by enabling the “extend luminance range” setting in your project settings. It’s also important to enable auto exposure in the project settings and make sure that it’s not limiting the max and min EV value.
Ultimately, the leaves of the Joshua Tree models I wanted to use in particular look super high contrast with very sharp shadows on the leaves and overly saturated relative to anything else in the level.
It’s also notable that the default scale of the trees appears to be about 2x to 3x too small for a realistic proportion in game. An easy fix to scale it, but it’s just something I noticed.