The Thumper was created with a purpose in mind completely different to that of other top-end weapons such as the Infinity Gauntlet (Charged) and the BFG9000. Thumper's main purpose is to be used alongside 1-hit capes at their respective zones, such as the Executive Cape at the Executive Zone. Thumper's massive area of effect, when combined with the 1-hitting ability of these capes, yields huge numbers of kills per hour.
It is also worth considering more niche uses that Thumper may have. It could be a useful switch in middling waves of the Arcade Minigame for it's unrivaled crowd control, or at Revenants for its ability to hit large portions of the cave at once. It is also fairly unique among weapons in having some fairly high defensive stats.