Stake launcher has insane peircing, and it murders the first few waves within a few seconds, and I didn't even mention the all-powerful Pulse Bow. Piranha Gun is a dungeon guardian killer.
For the few times you have all kinds of enemies in a straight line, I suppose the Stake Launcher could have its niche. How often is that, again? Moons, maybe... but don't most people use traps for the little small fry enemies and focus on the bigger stuff?
Pulse Bow did not seem all that powerful when I tried it. It has a cool ricochet ability, but that's about it. Oh, and it uses it's own ammo type, or shall I say, it seems to "forget" the ammo type you're actually using.
And the Piranha Gun... well, ok, sure you can kill the Dungeon Guardian with it... and... what else, again?
When you get to the end of the game when you're making these big decisions about what weapons you're going to use... you're probably thinking in terms of Pumpkings and Ice Queens, as well as helping burst down stuff like Everscreams and Mourning Woods faster than the traps can. But once the Pumpkings/Ice Queens come out, that's when you need something
good and as a ranged... I find the list rather lacking. If you want to stay alive, you gotta do a lot of dodging which doesn't give you lots of time to aim. That's when homing projectiles really shine, you don't have to aim, you just fire in the general direction of the enemy while flying circles around him. Below, the traps continue to mow down the small fry mobs while you work on the boss.
The Piranha Gun might sound good for that, maybe. However, you could also go Magic or Melee and do quite a bit more DPS with superior weapons, like Flairon, Razorblade Typhoon, etc.
EDIT: Reading the wiki, it sounds like the Snowman Cannon is probably the ideal choice... but wait... it is dropped during Frost Moon, lol. By the time you GET one of those bad boys... you probably are done, or near-done with the moons already, lol.