The point of an infinity gauntlet-type weapon wouldn't be to have balance. It'd be to practically have sandbox without having played sandbox before then, as they might not add an option to turn on sandbox in the middle of a character or world's life, like creating a survival character/world, then switching to sandbox. Also, it wouldn't be easy to get, locked behind killing a super boss multiple times to make it overpowered, making it a grind and a challenge of skill, though it would get easy after the first time.
If an infinity gauntlet-esque item were added, then, well that's the decision the devs made, and I trust in their decisions. As it would be the best weapon, all other weapons would be obsolete by the time it was acquired. Not only this, there's no one stopping someone from cheating one in. So, if a theoretical Infinity Gauntlet made it into Terraria, I'd like people to keep these things in mind. As this
is considered a sandbox item, speed-killing bosses with the Gauntlet would either be in its own category or ruled out altogether, as any other runs wouldn't be able to match the speed and deadliness of the boss killers. Secondly, what makes Terraria be Terraria is combat. Terraria isn't just a building game. It's a building game where 30 Harpies swarm you at once, threatening to kill, or at least annoy you. I stake my 2000 hours of experience that playing Terraria with a gauntlet would be easier to build in, but there wouldn't be the threat of death. Finally, having the Gauntlet may be a challenging final grind in and of itself, but once you obtain it, the Terraria progression system becomes obsolete. Simply go onto a new world with your Gauntlet character, deposit the Gauntlet in a chest, and bring your new character into the world, and you become a ultimate being of power. Of course, not bringing the Gauntlet into a world is a simple way to avoid this.
I think this is a good idea for what the developers could add instead:
Killing the boss unlocks an optional/toggleable Creative Mode for the character you killed the ultra boss with. As it unlocks for the player only, it cannot be transferred legitimately. My ideas for this creative mode comes with infinite non-Ore/material blocks (including wood, though it is a material), therefore allowing players to build infinitely. Secondly, it comes with a doubled or tripled maximum health for the player, alongside knockback resistance, making the game much easier to build in without dying. Bosses still take the same amount of time to kill, but the threat of death is lessened. The map is also completely revealed, allowing the players to find all the loot they need, preserving the fun of hunting for loot. Finally, the player is gifted with control over hostile monster spawns.