Much of the game's balance comes from what may or may not be bugs. Why don't we know if they are bugs? Because in the past, what we considered "correct" the devs have randomly noticed and changed, take for example the volcanic pepperbox's charge that pulled enemies. Similarly, the devs have ignored "bugs" that have been reported time and time again-perhaps these 'bugs' were intended?

-DA/GF were once the talk of the town; now they're once glorious projectiles are sucked into walls- even when said walls are behind the player. This also happens for other things as well, like polaris, callahan, the birds from AP/Sentenza...
-RSS can put 5+ projectiles into a single enemy, allowing it to be on-par with many 5* weapons, even against slimes
-The iron slug does not always cause its opponents to stagger, making it essentially worthless (getting fixed?)
-Alchemer bullets can ricochet internally within a single target, allowing alchemers to compete with argent peacemaker/sentenza in terms of single target damage.
-The bird on the charge of argent peacemaker/sentenza spawns slightly in front of the player, letting enemies that are at close range attack you while not getting hit enough to knock them back.
-Winmillion's charge can be canceled by shielding, and can be made to go in a different direction should the player turn while charging. Combined with its low damage output, the inability to shield directly after a charge makes winmillion's charget terrible.
-Jelly minis slip in between the "bullets" of dark retribution, helping to balance the item against ash of agni, perhaps an error with the hitbox?

Again, I don't know for a fact that these are "broken", because I have not heard either way from an official source; if anyone can think of any more things, feel free to post.