Now do 3 slams per year.
3 Majors per year is certainly an amazing accomplishment, but I don't think it has much bearing on consistency.
In fact, if we're going apples to apples, it would be the opposite, right? Assume Player A and Player B both have 9 Majors. Player A wins 1 a year for 9 straight years. Player B wins 3 Majors, then another 3 Majors 3 years later, and then another 3 Majors 3 years later. Player A is much more consistent, right?