I am pretty sure we do try to run Ray off of screens a number of times during the game.
The problem is, he is covered and Rondo ends up dribbling and having to shoot a long contested jumper as the shot clock expires.
Pierce's Iso's work a lot better because he has a chance to score, a chance to make a play for others, and a chance to get to the line.
A Ray Allen screen is just an open jumper.
KG down on the box is just a fall away jumper. (Teams do not double KG anymore, that time is over).
Isn't an open jumper from Ray Allen what we want? He's one of the greatest shooters of all time. Just an open jumper for Ray has a very good chance of resulting in 2 points and is a higher percentage play then a Paul Piece iso. If the Pierce iso did those 3 things you said I'd be semi okay with it, but it doesn't. It doesn't create for others anymore. Yes, he does go to the line, but he's not putting himself in the best spot for him to score. Let's face it, Pierce is guardable now. He can be defended. This team cannot have any sort of isolation from anyone. For this team to be successful you need to have KG, Pierce, Ray, and Rondo all taking shots within the flow of a set offense. There's about 5 players in the league you have run a team with a strict isolation. Pierce just isn't one of them anymore. Also, with most of the other players, Durant, LeBron, Wade, when they iso, they're looking to get to the basket. They're not settling for an 18 foot fade away jumper.