Here's my 2 cents.
Aaron Rodgers is still every bit the player that he's always been in terms of capability. Maybe he's slightly less dangerous as a runner, but literally I think that's it in terms of his ability to play the position. His arm looks great to me, he still flashes those wow throws, and he can still extend plays.
Aaron Rodgers is not doing a great job of running the offense as designed right now. When he does, especially in the early portions of games when sequences are scripted, the offense hums. They are 3rd in first quarter scoring. When they get beyond the script, things stall in a bad way.
I think this explains why fans are so polarized on him-- some see him make the wow throws and think "same guy as ever." Others see him missing open options and generally being inefficient and think "not the same guy." I think both sides have a point.
The reason for this is anyone's guess. Is he bucking against Petals' system?
I think it's far more likely that it's all just new. A helpful parallel, in my opinion, is the 2015 Falcons. That was Shanahan's first season there as OC. He was installing a new system with an accomplished, veteran QB. The offense was 21st in scoring, inconsistent overall, and the team finished 8-8. The next year, the system really set in and clicked, the offense was 1st in scoring by a huge margin, Ryan was an MVP, and then Shanahan got poached. And it wasn't like it all fit hand in glove. Both Shanahan and Ryan talked about how they had to compromise to make the offense work for both of them.
I'm not saying that the Packers are going to set the league on fire in 2020 the way the Falcons did, but systems don't necessarily take hold and flourish immediately.