Actually Eli Manning had 2 very good playoff runs, both leading to a Super Bowl win and the Superbowl MVP award. Go through the stats for those 8 playoff games and you will see. However, his other playoff appearances were bad except for last Sunday's in which he played well. (Unlike Aaron Rodgers whom I suspect is a robot.)
IMO, the Giants dramatically improved their defense this season. It's their offense which is pathetic. Their Oline gives the QB about 2.5 seconds to throw if he's lucky. Their #9 pick in the 2015 draft is about useless. They will not win it all again during Eli