There is going to be some natural fluctuation around the expected result. If a guy outperforms all the others by three standard deviations it might be an exploit, or it might be a 1 in 400 chance. In the real world it won't be anything like that clear cut, especially if the guy is trying to stay under the radar.
And, as I keep stating, debuff hacks are one possible play: there are many, many others. You don't have to restrict debuffs to your stampede pet for example. Nor do they have to be restricted to damage. Or you might not be using debuffs at all.