I think it is important to note that although the E3 graphics may have "looked" better overall (providing a better aesthetic and atmospheric feel), the new shaders resulting in the perceived "downgrade" may actually be of higher quality, technically speaking.
That does not however mean that the artists did a good job implementing the lighting in the final game, using the tools at their disposal. Far from it. They could have done a LOT better.
Modders like Essenthy and others have proven that it is possible to get a visual representation much closer to E3, far superior than the current vanilla look. CDPR themselves have proven this by implementing improved lighting in the B&W expansion.
Aside from increased number of particles and such which would impact on game performance (but isn't BTW impossible to add) CDPR can definitely give us improved lighting more representative of E3 - if they wanted to.
This is not just about "artistic choice" either. There are some technical problems with the vanilla lighting that were fixed by modders. Sadly, usually these improvements also introduced new problems, but this is because we as a modding community do not have the tools to edit lighting in the game. It has to be done by hand. Trial and error.
It's a strange thing. Since the game was launched, this has been the single largest issue people have taken with the game, but CDPR simply seem to refuse to fix it. They even showed us how they can do much better (B&W), but still they refuse to fix the lighting in the base game.
Maybe they will surprise us one of these days and provide an update with phenomenally improved lighting for the entire base game. That would be characteristic of CDPR.
One can only dream....