This may sound dumb or obvious, but when you rap over a beat, it’s like you’re adding another drum beat to the song, if that makes sense.
Therefore rap is for sure music.
I don’t love it all, but I do consider it music and an amazing Avenue to express yourself. I would argue that Rap as opposed to most mainstream music at its core is about the message the lyrics are trying to convey.
Example:
Edit: at least it used to be back in the 80-early 2000s. I hardly listen to new shit anymore hehe.