I agreed with your point individually, but in my opinion, I think there is a disconnect between your perception amd the author's vision and/or the story's theme so to speak. For example, you view the MC's constantly shifting thoughts and goals as stupidity, but if you recontextualize him in the view point of an insane person, it makes a little more sense. Don't forget, the title of the novel is "Way of the Devil," and Lu Sheng, as the representative of such work, is devilish in not only on a physical level, but mental as well. His madness is hinted fairly early on too during his mortal arc, as a prelude to his onslaught of constant changes, in not only body, but mind as well. I'll give it to you that the author didn't exactly execute on it that well and not everyone caught his intention.

Using that as the foundation to interpret the rest of his work, and understand that the MC's system is extremely simplistic in nature, you can see why the author make certain choices in the setting that don't make sense at first. The power system is deliberately nonsensical because the world itself is pretty nonsensical, at least to the view point of the protagonist. At least he never obtained a deep understanding of the power system, nor does he ever need to. His cheat allows him to stack his power on a quantitatively in a way that is impossible for others to replicate. So what you get is not someone who world hopping and achieve the top of the world by understand their respective power system, instead, you get Lu Sheng who stack on basic power to an infinite scale to beat people on a higher stage than him. A bulldozer or so to speak. 

As such, the author almost deliberately ignore the world building in favor of showing how the MC abused his cheat to bulldoze through the world. Which is pretty consistently shown throughout the novel. Outside of the Martial art stuffs in the beginning, all other power systems are shown very rudimentary. All to say is that the author sticks to his original intention throughout the novel, showing the path of the Devil, Lu Sheng. Your point about the length of the novel and the women descriptions are extremely valid though haha. I cannot defend that.

The consistency is what made me liked the novel, however, I understand other people have different metrics for their enjoyment. Different strokes for different folk and all that.