From my updated parser grabbing data on 341,159 valid plays, the aggregate average of all passing plays completion % is 53.4 rounded up and the average per play is 2.57 yards rounded up. I'm not posting this to say 4.6 sucks, but just that I wish there were more viable passing plays to call so we could have something resembling chess matches more.
This is from each completed full season starting from the XFL season 2041 and from the USFL season 1997 regular and postseason data only, and using excel's average function on the columns of completion percentage and average per play. The average per play does include the negative yardage from sacks. Almost every long pass has a negative yards per average because of this, but they didn't have great averages before that anyways.
Also for fun, I'll give a 4th round pick to whoever can guess out of the 148 plays I have data on, how many that have the first "target" be a WR where the play averages over 50% completion rate and averages over or equals 4 yards