IMO, comparing Lego sets and MOCs really depends on context and viewpoint. It really depends on what you consider to be good. Design? Complexity? Functions? It´s all up to what you´re looking for.
A MOC maker could model their MOCs after actual Lego sets, and the result doesn´t have to be more complex. Skill level should also be put into account here.
Yet, some Lego sets are terrible and I don´t think someone with basic knowledge of building could end up making a Good Guy 2008 remake, for example, without some sort of improvement.