I'm not sure what Reina's long passing stats were like, but Mignolet's have been piss poor this season. Something like 1/6 of his long passes find a red shirt, and he plays it long maybe 3 times more often than he passes short. That's giving the ball back to the opposition an awful lot. In the Utd game he misplaced a pass 17 times - a big percentage of our total. Against Swansea 17 of our 73 misplaced passes were from him. Against Southampton it was 17 of 105.
I haven't looked at other keepers in loads of detail, but a quick scan suggests that most keepers find a target with a long pass in 30-50% of situations. I remember people looking at his passing stats (and Begovic's) in one of the transfer threads and, from memory, Mignolet's overall passing percentage was around 50% at Sunderland, so maybe he'll improve as the season goes on.
Of course the stats just bear out what our eyes tell us in this case don't they? The ball gets played back to Mignolet and you're thinking "please don't fucking hoof it again". That's not to say that I haven't been impressed by him so far. He's definitely earned his wages so far, and he's gained us points in a couple of games at least.
I remember PoP talking about the difference between 'technique' and 'skill' in the past. I can't remember which way round it is, but one is the ability to do something in isolation and the other is the ability to perform that action under pressure in a match day situation. I wonder if we're just seeing the effect of Mignolet getting used to the challenge of playing at a higher level club. Kind of like a striker who struggles when they've got time to think but scores goals when they're acting on instinct. He's doing the reactive stuff brilliantly at times, but when he's got a few seconds to plan a pass he wobbles a bit. I definitely think we'll see improvements as he settles in at the club.