True Night's Edge

The recipe wants souls from every mechanical boss rather than one, so you cannot reach for this the moment hardmode melee starts hurting. By the time all three are farmed you are already close to Plantera, which leaves the sword a narrow window of its own. Build it anyway: it is a required part of the Terra Blade, and those souls have nowhere better to go at that point.

The swing drags a circle of purple energy that reaches past the blade and, more usefully, covers ground behind you. Something that got around your back takes damage without you turning to face it, and that coverage is the real upgrade over the Night's Edge. The limit is that the ring only bites a couple of enemies per swing, so a thick crowd still pushes through.

Each swing also throws a spinning green ring forward. It can land several hits on one enemy as long as that enemy is large enough to stay inside it, which is why the sword looks so much better against worms and the mechanical bosses than against a scattering of small things. It drifts with your vertical position as it travels, ignores water and lava completely, and fades after a moment, so treat it as mid range pressure rather than artillery.

Legendary is the roll to hold out for. Beyond that this is a stepping stone. Excalibur and True Excalibur occupy the same tier from the other direction, and once Plantera falls the Terra Blade absorbs both swords and makes the whole argument moot.