In my opinion, and that's all it is, I think most people are ultimately going after the effects of whatever problems they perceive rather than at the source itself. Again, this is all just my opinion, but I think the source of most people's complaints is Vince McMahon himself. Is it really fair to lay all the blame for whatever dissatisfies you on the shoulders of one man? Probably not completely but, then again, life isn't fair and Vince McMahon does have THE final say on what happens or doesn't happen on our TVs each week; sometimes it's a good thing, sometimes it's a bad thing, sometimes it's a mix of both. Any wrestling promotion or television program can only be as good as the creative team makes it and in WWE, Vince McMahon is the single person who decides that what goes on & what doesn't, who gets pushed & who doesn't, which storyline is given to which stars & which isn't, etc.
There are some unanswered questions about NXT that can only be answered as time passes by. For instance, can the show be as entertaining if it expands to 2 hours? Can they continue to use the same formula for success by making the most of the additional time as they do with what they currently have? Will the general layout, strategies and format of the show connect with a broader audience if given a chance to be exposed to it? Until some of those questions are answered, then it's just a lot of speculation right now.
Personally, I think the answer to those questions is yes; I might be completely wrong, but I have a feeling NXT would be embraced by fans, I think they could continue with the same formula that's helped make the brand a hit and I think they could make great use of the additional time. If all that does turn out to be correct, however, replacing SmackDown! with NXT will probably solve absolutely nothing in the long run because the core problem remains: Vincent Kennedy McMahon. People see NXT and they're encouraged by what many believe, feel and say WWE would be like with Triple H making the final creative decisions; that MAY be true but even if it is, it's moot right now because replacing SmackDown! with NXT as the new "B Show" makes NXT the main roster. That means that it won't be Triple H making the final creative decisions for NXT anymore, it'll be Vince and the same complaints the OP or others make in regards to SmackDown! will probably be applied to NXT before long.