I used theworse mod, it added things like the dynamic shadows, it caused little to no performance hit, far from unplayable and I don't have a high end pc.
2 things:
1. I wasn't sure what Watch Dogs mod you were referring too, but insofar as Witcher 3 is concerned, that one didn't add any of the effects that didn't make release. You were essentially saying that a modder replaced what CDPR downgraded, and that is not the case.
2. As for theworse mod for Watch Dogs, a mod I am familiar with since it was released, it absolutely has a performance hit, shadows always do. Fact is most of these mods have a performance hit to some degree.
Getting your game running optimally on as many systems as possible is the goal, that's the intent. Granted, showing off what you hope to release was/is not the best idea, it is understandable given the money at stake. But then reality hits and things have to change with only a limited amount of time to finish.
Downgrades aren't ideal and disappointing, but hardly unnecessary. Pretty sure given the option both developers would have preferred to release exactly what they promised, rather than deal with the feedback. Now people see downgrades everywhere, either because they blow things out of proportion or just want the attention that comes with it (probably both). In any case, it's something that should be common sense, things change during development, and not always for the better.