It is not similar to The Witcher 3 discussion at all. With TW3, the issue was that the final product did not look as good as one that was previously shown in order to generate hype. From what I have seen, nobody is suggesting Fallout's graphics have been downgraded, just that they are not that great to begin with(I haven't paid any attention to the graphics tbh). If anything, Fallout is learning from TW3 by not showing massively exaggerated graphics before release. This is a good thing and should be seen as a positive.