I blame Luka for the Porzingis thing. Luka + KP didn't work. Luka didn't like KP to set up in his favorite spots, so KP was just hanging around corner 3 mostly. He was also injury prone. The basketball public thought KP was a joke in Dallas.
And Luka's partially to blame for the Brunson thing. Luka kept the ball out of his hands. Brunson was a good 6th man. People thought he'd be a legit PG. Nobody saw this coming. The only time we got a taste of who Brunson really was happened in the Jazz series after the Mavs failed to extend him, and then the next summer was too late for Brunson, who wisely decided he didn't want to play with Luka. The FO still deserves the bulk of the blame, but I think this is part of the Luka experience that they were tired of. No matter what they want to do, their identity is Luka.