We have people working to solve these complaints. We don't stand by and accept them just because they exist.
Perhaps not in the context of all weapons, but for these biome weapons, obtained in the same manner, relegated to the same dungeon, it is absolutely unacceptable to introduce a weapon of one class without adding three more. The class inequality when you view the list of weapons in Terraria is much, much less obvious than when you look at just the four biome weapons that can be obtained in one world. "It's already unequal, so why not add to that?" ...said no one.
Absolutely true. Well, not exactly. They can make the suggestion, but they fail for the same reason. They create an imbalance and don't do anything to fix it. Add an Ocean chest with a melee weapon, an Underworld chest with a summoning weapon, a Mushroom chest with a ranged weapon, a Desert chest with a magic weapon (or something like that). And it works out, fine and dandy. But it is not acceptable to add one weapon alone. Absolutely not.
first off, the biome chest weapons are not necessarily the strongest weapons in the game. and each weapon(in the whole game, not just biome chest weapons) has different attack styles, so a scourge of the corruptor, for example, might not work well in certain circumstances that a death sickle would work great in, and vice versa. so people might complain that there are more melee weapons in the game than ranged weapons would be unfair, or that there are no ranged, magic, or summoner variants of copper, iron, silver, and gold armor is unfair, etc.
to make the game completely "fair" to each class in the game, all the time, would require redigit to make sure there are exactly the same number of melee weapons in the game as ranged, magic, and summoner, and the same number of melee armor pieces in the game as mage, ranger, and summoner, and the same number of everything pertaining to each class. seems impossible.
imagine there are 2 biome chest weapons for each class. everything is perfectly balanced. then, someone makes a biome chest suggestion. everyone criticizes it because it's "unbalanced." you can't expect people to come up with variants of their idea for each class every time they get an idea.
if someone gets an idea for a melee weapon, by your logic, the game is suddenly unbalanced due to the fact that there is now one more melee weapon in the game. it shouldn't be a requirement for people to post their ideas in groups with full support for each class.
imagine someone comes up with an enemy that has melee resistance. by your logic, melee is now underrepresented as there is a new enemy that is resistant to melee attacks. should the original poster make it have equal damage resistance against each kind of damage? no. it's impossible to make it "equal" for each class for the whole game, as different classes are specialized for different tasks and scenarios.