At it's deepest level "modern jazz" is the expression of complex human emotions musically. While I adhere to "Wikipedia" for the definition of many things, I jump ship when it comes to "modern jazz"; that's because it's a departure from what originated in New Orleans, where they claim is the "birth place" of jazz.
According to me and my ears, no one contributed more to "modern jazz" than Charles "Yardbird" Parker; all you have to do is listen to jazz before and after Charles "Yardbird" Parker. He didn't just help to invent "Bee Bop" he changed things in a way that can heard, as opposed to explained.
He could even incorporate "Bop" in standard tunes like no one else; his Charlie Parker with Strings is the best example of this;
https://www.youtube.com/watch?v=DmRkZeGFONg&list=PLqzxGGRskMsArMdq06cOawHAbO2kBWfmD
As I stated at the beginning, jazz at it's "deepest level" is the expression of complex human emotions. Before one can express these emotions, one must first have them. Never the less, that requires an incredible talent; one that doesn't often come along.
I'll give you examples of the expression of profound emotions: Bobby Timmons "Moanin" is a very clear example, he is also in the top tier of artists who have this capability.
https://www.youtube.com/watch?v=cNjRQo-zpKA
I wrote about a close personal friend I had who was also a "Blue Note" recording artist. I will never give his name for two reasons, maybe I revealed too much personal information when I wrote about him, and last, the incredible music he was playing when he shared my apartment was never recorded; therefore I can't prove that he was much more incredible as an artist, than the music that's recorded on Blue Note.
I stated that he had no formal training. That was interpreted as musicians who don't go to "formal" school are better than musicians who do. That was a moronic interpretation; not going to a formal school is a severe handicap; it's necessary to write music in order to be successful. Musicians skipped formal school in times past because of financial limitations.
Everything that happens in this country is related in some way to everything else; those with a myopic view of things are totally unaware of this. If one is financially secure, and focused on turntable setup, they would hardly be aware of the socioeconomic condition of the "lower middle class", but whether they are aware or not, that affects the quality of jazz in this country because that's where it comes from.