Octavia is a great Warframe and Lots of people enjoy her. One of the reasons a lot of players enjoy her is because they are able to make the music they want to hear. Her abilities synergize really well. Her 1 gives percussion. Her 2 plays bass. Her 3 gives melody. These together can make a cool song.
However, sometimes subsuming abilities best fits the mission type or play style you want.
The Problem: Removing a ability also removes that music sound from the mandachord and you are left with 1 less instrument and the whole song sounding empty.
Ex: I replace Octavia's 2 (resonator