One remark (that may seem like a nitpick, but is in fact crucial) : composition doesn't say it "is a kind of", but rather "it has".
It's the two most fundamental concept of any language : to be vs to have. Now it may or may not be just a philosophical difference and bring no practical consequences to a computer program, but at the minimum one can say it expresses two different concepts.
Only if A: composition can't do the job somehow and B: you can't use perfectly normal factoring tools to do the work.
While I will tell you before anybody else complains that there is a non-zero percentage of the time that will happen, I will also tell you the average person who has never tried Go yet complains about its lack of generics anyhow will overestimate the amount of time that happens by a good order of magnitude or two.