1) The amount of ball speed necessary to make it useful is very high. If the ball speed isn’t high enough, the ball doesn’t go far enough to make it different than the next higher numbered club.
2) These clubs have also been affected by VLD (vanishing loft disease). Over the last couple decades, club manufactures have consistently strengthened the loft on its irons to claim they hit them longer. They’ve strengthened them so much that a whole new club had to be added to the set. The Gap wedge. Not to long ago, the PW had a loft around 50 degrees. Now it’s 47ish. That is almost a full clubs worth. Today’s 4 iron is pretty close to a 3 iron, so in most set make ups, that club should go.