OK, but here are your outcomes if you are good at X and need X and Y:

You do X, hire Y - You have one skilled person, one question mark.

You do Y, hire X - You have one unskilled person, one question mark.

Seems pretty simple to me that the first is better. I suppose that you could make the argument that Y may be easy to pick up, but if that's the case it should be all the easier to just hire someone else with a proven track record.