It shouldn’t be necessary to play around with lighting when upgrading three.js versions, we don’t intentionally make changes quite that capriciously. 
Really looks to me like your first scene uses a gamma workflow and your second uses a linear workflow. If that’s the case, maybe you should remove the renderer.outputEncoding = sRGBEncoding line?
Aside, I personally think the 2nd looks better, with exception of the Youtube logo. Note that if you are using sRGBEncoding for the output, you should also set texture.encoding = sRGBEncoding for any texture you add to the scene yourself, if it contains color data. In the code you shared, iconMesh.material.map.encoding should be set to sRGBEncoding if the renderer output is sRGB.
If that’s not helping you may need to share a live demo, I think that’s all I can guess by looking at the screenshots.