Convergence. That the word.
I agree that one device which wants to do, badly, three functions. Is not good.
However, my iPhone can be used as a phone, a mini computer, taking notes and allowing me to keep my appointments, agenda, read PDF and e-books. Listen music, watch videos, take pictures and, eventually, videos. Yes, the quality is not the one of a computer for documents and heavy work; the music is not such as listening to the opera, and video not like being in a theatre.
Or taking picture is not like my old reflex.
However All is compensed by size, portability and the ability to have everything right there at the right moment.