Well, first, let's note that Stafford is not Brady.
Second, let's note that Johnson is drawing double coverages by the best pass defenders on the field, while Gronk is not.
Third, TDs are a relatively inconsistent number, as even the current single season record holder, Randy Moss, demonstrates when you look at his career numbers. Yes, he's got the record with 23 catches in a season. He also had years with 7,8,3 and 5 TD receptions, with a couple of those numbers coming in his prime receiving years.
Fourth,
Graham: 75 catches for 1046 yards.
Gronk: 65 catches for 928
So, going with a "look only at the numbers" approach, one can easily argue that Graham is at least the equal of Gronk. I know you're going to try arguing that Gronk has more TDs, but Graham has more catches and more yards. And, after all, it's all about the numbers, right?