Yes it is.

Manning apologists and stat geeks alike will pounce on anyone saying this and point out things like his passer rating, DVOA, EPA/G FLORBP, BBQ, blah blah blah whatever stats they can pile on to hide what actually happens. The truth lies not in the stats but in the film. Which is why the apologists and stat geeks usually win this argument--who's really gonna go over film from 24 playoff games to answer this?

Well, some people have, and what they've found is that it's not that Manning just turns the ball over or throws some incompletions, it's when he does these things that cost his team the game.

You get very few games like the 2014 divisional game against the Colts where he plays poorly the entire time and never puts his team in it. Look instead at Super Bowls XLIV and XLVIII, the 2012 divisional game against the Ravens, the 2011 wildcard game against the Jets, the 2009 wildcard game against the Chargers, the 2008 divisional game against the Chargers, the 2006 divisional game against the Steelers, and the 2003 wild card game against the Jets. In almost all those games Manning's statline is excellent or at least decent, yet in each of those games he played his worst when it mattered the most. Just watch the film and you see that the interceptions and incompletions come at the most critical moments of the game. The multiple pick-sixes are the biggest problem. Manning throws more than a few of these when he's in or nearing the red-zone. Instead of giving his team 3-7 points he gives the opponent a free 7.

That won't show up in some fanboy apologists 'advanced' metrics analysis of Manning, but the film doesn't lie. When Manning isn't beating up on some AFC South toilet of a team in a warm comfy dome and there's big stakes to play for, he makes some really poor decisions.