But it has arena trap, making it the only physical revenge killer that will guarantee a shot at hitting or at least effecting your desired target, as opposed to others that will only guarantee you get off an attack on their switch-in. Memento also gives it the option of turning the game around from a failed revenge-kill situation, again handing you complete control of the situation. Dugtrio's reliability isn't in its power, or obviously its defenses, but its speed and ground typing, as well as its ability to guarantee a result that you can choose freely from, even if the result may not be as crushing as something from garchomp.
In a team that NEEDS things like magnezone or shanderaa dead, instead of just hoping they won't switch out, there are quite simply no other options in physical revenge killers. EDIT: though I guess you could use a snorlax with pursuit for shanderaa, but dugtrio covers more than just dark-weak pokemon.
