Nah hear me out, the catachan dagger is op because it shreds hordes without them being able to hit you back with all the dodging. It even handles armoured enemies better than my lasrifle!
Seriously though i dont get why the flamethrower would be considered a problem, it lets zealots invest in becoming full melee specialists at the cost of long range precision. Thats like if the Vet had to trade their rifle for a pistol to take the power sword.