I really liked their relationship, that was one of the strengths of the film. At least from alitas perspective. (didn't care about him as a character)
and yeah when he was rebuilt and then climbed up the pipe and then died, it was all a bit quick, felt like some scenes had been edited out. Which may not have made it better if they were in, but no that bit didn't really work for him as a character.
It did work in terms of the affect it has on Alita and that was what I thought was important. Seeing and believing Alita's reactions to events in the movie is enough for me. The entire film is held together (imo) by the character of Alita (and, I suppose in part by Rosa Salazar's performance).
Also can I just say I really liked how fast the credits went. More movies should do that.