What's wrong with Devin Booker, and how concerned should Suns be over his slow start?

It feels strange to nitpick a team that's 9-3 after such its opening-month gauntlet, but there's no denying that Devin Booker hasn't looked like himself so far this season.
Whether it's a few memorable clunkers, perpetual angst over whether or not he's wearing a headband, or simply the fanbase's repeated glances over their shoulders at what other shooting guards like Donovan Mitchell and Anthony Edwards are doing, Book's start to the 2024-25 campaign has underwhelmed.
Despite how overblown these Booker concerns have become, despite what he's provided as a playmaker who's trusting in Kevin Durant and the improved depth around him, and despite the season being a measly 12-game sample size, it'...