If you take a top 20 player off a 50 win team, they're going to be much worse. That's almost pretty much universally true.
The Suns have a good backup but it is easy to have a good start or two, try doing it when the other team has seen you play 38 minutes a game over 2 weeks. He's a backup for a reason.
And Booker would have to do way more playmaking without CP which would really hurt his efficiency (the only other offense creator they have)
Not to mention all the intangibles he brings like experience, leadership, motivation, poise, coach on the floor which is immensely valuable to a young team.
This is a bizarre discussion to me but to each their own.