That's one of the great homebrew myths that dates back to
Lloyd Rigby's paper of 1972. He added the same amount of different alpha acids to wort, but didn't allow for the fact that cohumulone has greater solubility and so greater utilisation than the others, so the cohumulone gave a beer of significantly greater bitterness. Thinking the bitterness was the same, Rigby interpreted the greater bitterness of the cohumulone beer as coarser bitterness.
But it's complicated, and people continue to debate the nature of bitterness - probably the best single thing to look for if you want smooth bitterness is a high proportion of beta acids relative to alpha (which would put the new Hopsteiner hop Contessa high on the list?). But it's very much a question of personal taste - some people like that raspy bitterness from eg Target, others prefer it smooth, there's no right answer (which is why commercial brewers like Fuller's hedge their bets by blending both).