I guess I don't know what to think. These are all things I've heard over the years.
1) Brady was a system QB, it was really Belichick.
2) Brady doesn't need the talent, he makes guys like Chris Hogan work.
3) Brady didn't do well last year because he didn't have the talent around him.
4) Brady's cooked. You could see it last year.
Then he goes to a new team, new system, new coach, no preseason, limitations on practicing....and puts up a great year.
Brady is a great QB. He has often played without great receivers. In the Patriots system he made that work because it was about precision and timing. The basketball equivalent of a perfect backdoor cut run by Princeton. He did have Moss and Gronk who could do more, and guys like Branch, Welker and Edelman who got open with superior quickness (if not straight line speed).
Arians runs a vertical passing system that relies on talent at WR to beat their man. Brady had a whole bunch of early hiccups adapting to that. As he became comfortable he was very good at executing it. He has 2 good TEs, three very good WR, 2 good RBs and a good OL. That offense is loaded.
Brady was not good in 2019 because the OL was obliterated and he's a human statue. Running an offense that is based on timing and precise route running, with pre-snap reads doesn't work if they other team can blitz you every down and get to you in about 2 seconds. It's worse when the receivers are young and don't know your pre-snap reads and route adjustments. Even then he threw for 4000 yards.
Miami fired their OC before this season. He was a Patriots guy. Flores said he can't run a Patriots offense with young players. The trend is away from complex pre-snap reads and adjustments, where Brady and Manning were the best ever, to post snap adjustments. Defenses disguise coverage so well that the adjustments frequently come post snap. Improvisational, athletic guys making plays. You can see it with most of the QBs still playing. Mahomes, Allen, Mayfield, Jackson etc. QB mobility, and read option means the offense is changing the play post snap. Brady can't run that. Brees can't run that. Rodgers probably can.