Calvin Johnson is absolutely dominant and a great player but Randy Moss changed how defenses play in the NFL.
Nobody in history affected defensive gameplans than Moss despite the fact that teams knew he was going to run one of at most 4 or 5 routes. Who cares if he didn't run slants or go over the middle when he took at the very least two players with him on pretty much every play.
Calvin Johnson is one the best WRs of the last 5 years, Randy Moss is one of the best WRs of all time. This isn't even close IMO