It is hard to reply since you change your post and your english is hard to read.
Your singer analogy does not fit. Developing a vn is tool usage. Singing is skill and talent. The wood analogy was better, but a game engine is actually a valid tool to make a game, and not some spoon. Of course one might build a custom tool that might be even better. But why? The story will not get better because of it.
It might be of interest to you, that you absolutly can supply your own code to use in most of those engines, even developed in rad. You use libraries, why not use the game engine library?
Do not scoff on developers for wanting to use an easy to use tool that was designed for the task, instead of using a general purpose tool. They have to do the writing and art and many other things as well.