Seems like QBs are credited for bad throws every time a pass goes incomplete. Many such passes are due to receiver error, or just bad luck (trips, stumbles, uncalled defensive penalties, etc). Lots of perfectly thrown passes turn in to "bad throws" due to missed timing which can happen AFTER the ball is thrown. QBs are tagged with every interception, including tipped balls the receiver simply did not catch properly.
There has never been a QB born that didn't have "flaws" and/or limitations, same as receivers, and same as pessimists that only remember unsuccessful attempts.
70% is a high completion rate for any QB.