Most of these aren't even vanilla and I have no idea what their properties are like in whatever mods they came from (which can be any of numerous mods), and otherwise they are theoretical ("overpowered gold" certainly can't be gold items with max-level enchantments, and what are "useless tools").
That said, nothing beats a Sharpness V diamond sword in 1.6.4, which deals 14.25 damage (vanilla displays it as +7 damage, which is 8 when added to your unarmed damage; they didn't show the effect of enchantments until later, and only since 1.9 has the total damage been displayed), and armor likewise reduces damage by a constant 80% no matter how much damage it you take (the only protection advantage Netherite has over diamond is +3 instead of +2 armor toughness, which means that instead of every 4 points of damage penetrating 1 armor point it penetrates one for every 5 - which of course means it will still offer less than 80% damage reduction for any level of damage taken).
Also, a combat snapshot nerfed the damage dealt by weapons by one (two relative to pre-1.9), meaning that if it also affected Netherite, which wasn't added yet, it would deal as much damage as diamond does now (or an unenchanted iron sword in 1.6.4).
Of course, if you are counting modded items there is TMCW's amethyst, which deals the same damage as diamond in vanilla but has 3 times the durability, including an armor durability that matches tools (4686 durability for tools, 4500 durability for armor, all pieces being the same), if not as protective since I nerfed player armor to 3.33% per armor point (damage/protection/speed for lower tiers was nerfed; armor/weapons used by mobs are actually stronger than vanilla diamond, in contrast with the 1.9 combat changes which weaken both players and mobs), or as easy to find since while it generates in the Overworld it is 8 times rarer than diamond across most of its range (interesting fact - diamond is actually rarer than Netherite/ancient debris at its peak layer, and it is much easier to mine Netherrack than stone, and while you need to mine 4 debris per ingot you only need 1 ingot to upgrade items. Put Mending on it and you don't need anymore at all, while TMCW uses the pre-1.8 repair system so you need to keep finding more).