Seems more of a function of Getsy calling plays than Fields unable to make the throws though. We know Fields can make the throws, if he sees them and actually pulls the trigger he is has been very efficient with the down field throws (I think), but since he can't be trusted to pull the trigger either due to processing time or a bad line Getsy has to call quick screens and other short plays to generate offense. With Bagent, we simply do not know if he can effectively throw downfield.
Anyways you know all this, just rationalizing why Bagents AirY/A matters and Fields' doesnt.