1. I think you misunderstand me. I am not interested in distillations and commentaries. I am interested in building upon the works of past philosophers, improving their weak arguments, supplying better arguments that they missed out on, finding better examples than what they used, and finally going past what the said, and saying even more. The replacement of Nietzsche's books should be books that say somewhat similar things, but which are better arguments than Nietzsche. This must be possible for any intellectual discipline, because any such discipline by definition must create transferable knowledge and skills. And if you are not, the problem cannot be with the character of your intellectual discipline, but with the social structure and practices of your discipline.
2. To follow upon point 1, and to answer your points 2, take the example of GR again. What Einstein wrote is simpler and probably easier to understand than good modern graduate textbooks on the subject - the latter have far more sophisticated arguments, and they go explore the area far more than Einstein ever did. Because of course, physicists and mathematicians kept building and improving.
Similarly, what I expect is that philosophers should constantly be making better and more sophisticated arguments, that require more and more skill and acumen to understand. But a beginner starts with very carefully constructed arguments that easy to understand, yet astounding, and as her skills increases, she is given more and more difficult arguments to grapple with. this is how things happen in other intellectual disciplines by design. But not in philosophy, and I truly don't understand why.