I know this isn't the point and I know your not saying Matuia is a bad defender but even though he missed 8 tackles last week this doesn't indicate how good he is defending on tha left edge.
Now he is one player that comes out of the line to smash forwards but unlike someone like Blair, he does it more in the middle of the field when their are defenders around him to clean it up. This is controlled aggression but of course this style of play is going to lead to more missed tackles. The stats also don't tell you about the 2-3 cover tackles he made and how he slides well across field to shut down an opposition raid even if he doesn't physically make a tackle. Compare this 3 miss tackles Morgan made but between him and Sio they let in 5 of the 6 tries (Barba, 2 to Morris and Wright). While Morgan didn't miss the tackles his poor positions creates the over lap and its as easy as through the hands.
Of course Reni is being used as a shooter, which is the best way to protect Sandow in the line. It's no coincidence that he's missed 6 and then 8 tackles since having Sandow positioned outside him in defence.
Morgan reads the defence just fine. He can't just sit on his opposite number all game; he has to adjust to the men inside him or the breaks will be made there instead.
Against the Bulldogs we had to compress tightly because of that Barba-running-behind-his-own-man play. As Jason Taylor said, it's indefensible because it's illegal.
Morgan has copped a bad rap for having to defend next to Sandow earlier in the year, but being used as a shooter makes everyone look bad - it happened to Blair when he played right centre, and even Willie Tonga (a good defender, whatever people say about his attack) was left in no man's land a few times recently. Now it's happening to Maitua.
The only player who does it well is Ben Smith.