If someone can't play piano, and another person can, then yes, that latter person is a better pianist.
But artist and even musician mean different things. Saying that someone is a talented artist suggests not just that they are grade whatever in this or that, or they can do a good cover of whatever on guitar, it means they have an understanding of music. They are original, can feel and 'see' music, they respect what music means and what it can do. Sometimes, if you're stretching it to extremes, all a brilliant musician is their music etc blah. In that respect, MJ ****s all over Justin Bieber.