"Running isn't as easy as it looks" - Eli Manning, probably.
On average, it's fair to say that defenders have a harder job than offensive players. Rule changes over the past few years have favored the offense. The NFL knows that high-scoring games attract attention, and the easiest way to generate more of those is tweak the rules to make it easier for offenses to make big plays. However, the defense always had one advantage; numbers. With five offensive linemen and a quarterback dedicated to every passing play, the defense could rush four players and let extra guys play back in coverage.