The idea that an offensive coordinator is sitting in the press box saying... wow we can throw it deep because the football has a pound and a half less air in it is completely stupid. I’m sorry. It just is. I’ve not played in the NFL, but I played a lot of quarterback. It is a stupid statement. Period.
Reality #1.. Lots of deeper routes are called on any given pass play & it's quite often left up to discretion of a veteran Q as to whether he will go deeper, shorter, or a "check-down"...
So you're assumption that it's all left to the offensive coordinator as to whether to go deep is off-base...Brady may have had ... and likely so... options on that 30-yard lst qtr play...and it would have been up to Brady's confidence level as to whether he would throw deep or go shorter route receivers...
Just like a Major league pitcher, who might know he's got a baseball all cut up and easier to "junkify" would have more confidence in throwing such a junk pitch in a key situation.
The key factors anybody associated with the offense is going to consider in pelting rain conditions is the catchability of wet footballs ... and if somebody knows it's more catchable, it simply increases the confidence of the person making the play.