A pathetic o-line and an even more pathetic RB is the main reason for the poor performance of McCown....
I believe he has shown a strong arm with great running skills... he does miss some reads, but with no running game to support him and a mediocre O-Line (at best), teams are knocking the nuts of him.
I still see the pathetic output of our RB situation as the #1 issue, o-line #2... you see the same thing in Miami, except they are focussed on fixing the RB and O-line problem.
Until these 2 areas are fixed we will continue to see our QB and WR's getting malled, beaten and clobbered... when they're not running for their lives !
We have excellent WRs. Perhaps a young core that is better than 80% of the teams in the league. These WR's can make even a bad QB look excellent. But without the protection, support and game planning brought on by a successful running back... teams will smother our o-line with a pass rush designed to mall the QB while he runs for cover trying to find a receiver that is double teamed... we need a running back that can force a defense to (at the very least) pay some attention to the position.