Its Op and clearly a mistake.
Now that might be true, putting it in a similar place to the hoik. But that doesn't make it any more balanced. It still SHOULD be fixed, even if they refuse to...
Ok, then. I'm going to explain exactly why I disagree that it's unbalanced.
This is Mappy's video explaining how to make a Dungeon Guardian farm using the Jousting Lance. At a glance, we can see that it requires a Bottomless Honey Bucket, hoiking, several teleporters, bubble blocks, the Inner Tube (but NOT the Mollusk Whistle), and dummy ghosts. The setup is very specific, can only be done in Hardmode, takes over a minute to actually reach top speed, and requires the Mechanic to be freed, meaning it cannot be done on a world that the Dungeon Guardian still exists in.
This is the simplest method to do this glitch, one that Mappy said is "sweat-free," and it requires a lot of game knowledge and more than one exploit. It's safe to say that absolutely nobody will stumble upon this in their playthroughs; in fact, it's safe to say that absolutely nobody will even think to do this without indication that it's possible. The barrier to entry, both in accessibility and convenience, is pretty damn high. And for what, to one-shot the Dungeon Guardian and get a Bone Key? When you could also just kill the Dungeon Guardian without it, with much less setup and possibly even faster overall depending on which weapon you used?
But maybe you could use this setup to cheese bosses? No, I don't think that's very feasible either. Bosses aren't going to sit there and let you build up speed for a minute. In lower difficulties, this setup isn't at all easy enough for it to be preferable for killing bosses, and on higher ones, you'd still be better off making an actual build and fighting the boss normally. There are quite a few bosses it wouldn't work on at all. Plantera doesn't get close enough in phase one, Lunatic Cultist doesn't get close to you at all, trying this on the Pillars would just result in you getting swarmed by enemies, and Moon Lord also doesn't get within jousting lance range of the player until all three eyes are downed. Not to mention that you'd have to rebuild the entire setup every time. And all of this is assuming that people would even want to do this; I'd imagine most players would rather fight bosses "legit."
In short, this exploit may output the highest damage in the game, but it's highly impractical, extremely specific, time-consuming, requires knowledge of several exploits, leaves the player a sitting duck, and doesn't work on the endgame bosses. There's a reason it's only used to kill the Dungeon Guardian. I cannot call for the removal of something this silly. Just leave it alone.