Pretty much this. Since I watched the game in person I can definitely confirm that it was the defense that was the real reason they lost. Sure the offense could've been better as well, but if their defense was on point they could've weathered that storm. I will give credit to the Suns, their ball movement is exceptional and they were making the right reads every time it seemed like.
After about 2 possessions I could tell the hard hedge/trap scheme on the Suns PnR was not going to work out well for us. Sure enough CP3 shredded us on that time and time again, but it wasn't just him, the whole Suns team had no issue passing to the roll man and then hitting the open shooter on the swing pass. CP3 didn't even have to be in the game and it was still happening. Ayton was basically a non factor for most the game being in foul trouble a bunch. Didn't matter. Suns had a stretch where CP3 and Booker were on the bench and their lead kept growing. To me, that's the most telling thing about the difference between us and them.
Yes the Bulls are missing most of their top defensive guys, of course that will make a difference. But it shouldn't make suddenly become the worst defensive team in basketball. I'll give Javonte credit, he's all heart and hustle out there, but he's constantly in "chase" mode on defense it seems like. He's not really going to "put the clamps" on anyone. Positionally he's great, but he's a SG playing PF most of the time. And unfortunately he's not a great shooter either. And even so, he's just one guy. Defense requires all 5 players to do their part. Slow rotations were very very common the whole night. It might be easy to blame Vuc for a lot of things at face value, but honestly he was doing everything he could defensively within the scheme for the most part. One thing I will blame Vuc for is bad shooting, but it's hardly a new thing at this point. He had one play I think in the 4th where he actually aggressively attacked Ayton in the paint and got a layup and I was just like, needed that 3 quarters ago Vuc.
Also TBJ looks more and more disappointing the more I see him play. He seemed great last year, but this year, nope. I'm all for giving Malcom Hill more of his minutes because at least he seems to make shots. This is probably all some sort of confirmation bias though and I'm sure the numbers will tell a different story.