I mean Mikal Bridges, Kelly Oubre, Ricky Rubio, and Aron Baynes are all good defenders. Ayton's not quite there yet but his defensive potential is through the roof and he improved greatly as last season continued(constantly practicing with Baynes will benefit him). Tyler Johnson and Dario Saric are average defenders at best and Devin Booker and Frank Kaminsky are poor defenders.
That covers all of the rotation players that aren't rookies. To me that doesn't look like a poor defensive team.
You only really have 2 guys on the squad that you can for sure say are bad defenders, everyone else is arguably at least average and some with potential to be great. But people will assume this is the same squad as last year even though it's almost a completely different team.
TJ Warren was one of the worst defenders in the league and he's gone. Dragan Bender sucks on defense and he got replaced. Ellie Okobo was horrible defensively and he'll likely be cut before the season starts. And guys we were playing for the first half of the season like Ryan Anderson, Tyson Chandler, Trevor Ariza, etc put 0 defensive effort when they were on the court for us. They didn't care at all about trying to win. This is not the same team as last season.