FL_Ag1998 said:
This show could have gone two routes....1) Danny comes back as a badass who's spent years delaying his revenge against his parents murderers so that he can be fully trained and prepared to take them down....or 2) Danny forsakes his training at a semi-early stage to seek his revenge, gets his butt kicked, realizes he needs to complete his training before exacting his revenge, yada, yada, yada.
To be completely honest, the show was so badly written that I'm not sure which route the writers took, but either way, they did a pisspoor job of conveying it.
If they had gone option 1, then the show should have been over in like 5 episodes and The Hand should have been destroyed in New York along with Colleen's Hand group as well. I think they tried that, hero smashes everything in his way, in Luke Cage and that's how we ended up with Diamondback and Shades in the later half. Cottonmouth was probably the best part of that show. It's a shame they killed him off.
A large issue is that they never really detailed why Danny left like redline said, and I don't think anyone will disagree with. His reason for leaving is just never really defined, and is a hanging question. The other issue with Danny is that he is written to have never really matured beyond being a teenager. Which is seemingly a stark contrast to his friend Davos who, despite having some kind of long running envy which caused them to feud, is more mature.