It takes a great composer to create a fine set of variations, because this does not demand pure invention so much as the ability to see the underlying possibilities of a single idea. Lesser composers can construct their music by the use of more material, which provides the opportunity for contrast. Nevertheless, a continuous succession of new ideas will not prove satisfying, so repetition of some sort is necessary.
By that definition, that means that any number of us who play Irish trad are great composers. Go us!