I mean he's not a new addition. That's an excuse we can use for Brunson who still looks less lost on defense than Cam.
To be fair though, he was starting to show a lot of promise last season right as he got the shoulder injury and then he couldn't practice the rest of the season. I also think he looks like he's pressing moreso than lost. He's trying to make the play, which means he'll try to chase over a screen when he should switch or slide into a passing lane too early.
It also looks like the scheme is changing slightly compared to last season (Randle is switching more, Centers are dropping even faster). I like that stuff for the long term but everyone's gotta adjust. Sims' hedging was pretty weak in his few minutes and Hartenstein kept losing position to rim runners with enough momentum to bump him off.