I've said some of this previously...
To me, Brady's strength has never been the long ball. This is not to say that he's never been "good", just not as elite as he has been with short-to-intermediate quick throws and timing throws, and most of the more aggressive passing attack since 2007 has been based on him making a quick read at the snap and getting the ball out lightning fast to a short/intermediate, "just open" target before the defense has a chance to recover. As AWTE has pointed out in the past, many QB's read progressions start with "long" and drop back to intermediate and then short. Brady's reads were almost always "short-to-long".
Now Brady did appear to be "elite" with the long ball in 2007, but a lot of that was due to Moss' exceptional ability to "see" the ball in the air (much like Ted Williams' exceptional ability to "see" the pitch) and make subtle adjustments in speed and stride to get to where the ball was actually going - spot-on accurate or not. Before his injury, Gronk actually showed a bit of that ability, but it wasn't there in the Jets game at all. And, neither KT nor Dobson are consistently close to grasping those adjustments yet.
Second point is that I think that Brady has been throwing deep in a higher percentage of his attempts than in the past, though I have no stats to back that up. While it's true that a significant portion of the sacks/hits he's taken this season have been due to OL breakdowns, more of them than in the past, I feel, have been due to Brady hanging on to the ball a bit longer, looking for that deep throw. Then, when he tries to get the ball to a different read - short or intermediate - the D has had time to recover. IOW, on an increased number of pass plays, he's reading long-to-short now.
And part of the problem with THAT is that I believe that Brady's accuracy has always suffered a bit when he's taken more time than less. I believe he may have a tendency to overthink his throws at times when he holds the ball for awhile, and I also think that has an impact on his mechanics (and a consequent effect on his accuracy). When he's in snap-read-throw mode, his mechanics are more a matter of muscle memory. Back in 2010, he appeared to be having difficulty finding Brandon Tate on deep throws (plays that took awhile to develop), but, on one play I remember, Brady was forced from the pocket as protection broke down. He scrambled first to his right, then cut back left. Tate, who'd initially been running a deep post was smart enough to come back a bit and mirror his QB toward the sideline. Brady, running as fast as he ever could while looking elsewhere, suddenly saw Tate and instantly threw a 30-yd bullet right into his hands. No overthinking about that throw - he just did it.
So, perhaps a subtle-but significant change to the offensive scheme, in combination with a whole bunch of new targets who he's not sure of yet, have aggravated that overthinking tendency with consequences to his mechanics and accuracy. One age-related factor may be that he's not quite as adaptable to new circumstances as he was when younger.
The above isn't intended to be a whole-cloth alternative explanation for Brady's woes, or any kind of excuse, just an exploration from a slightly different perspective. In any case, to me it seems to beat the f**k out of simply saying, "He's getting old and is in obvious decline."
