One reason baseball is better suited to statistical analysis is that it is basically a series of ONE-ON-ONE events. Pitcher throws to hitter, they're the only two involved. You can say Mike Trout won the AB against Justin Verlander because he hit a homer. If Brady throws a TD pass, at least six other players had to do their jobs to make it happen (5 o-linemen and the receiver). It was probably all eleven players in concert that made it happen (slot receiver picks the defender, play-action fake carried out by RB, TE drew the safety, etc.)
Also, saying Brady's "rating" was XXX, and so-and-so's rating is YYY is TOTALLY MEANINGLESS. The QB rating formula is based on some statistical targets that were established over 40 years ago. Any stat system that says Colin Kaepernick is a better QB than Dan Marino or Troy Aikman is a joke.