just curious, not at any specific level just overall
If we're excluding the obvious super low level stuff that's meant to be replaced by objectively better items as soon as possible, my votes would go to the Ramshackle Power Armor, Frozen Spire, and Chaingun.
The Ramshackle Power Armor is here because it's so incredibly disappointing considering how awesome a suit of power armor should be and the fact that it's the only armor piece of its kind in the game. It's not bad by any means and it is cool how it has a unique scene with the Forgehound, but it just needed way higher stats to compensate for the massive hit to evasion.
The Frozen Spire makes the list entirely because there's just no identity to it. Visually, it's such a cool, unique weapon that you can pick up from Tuuva at high affection, but it's just completely useless in the face of the sheer number of weapons that outclass it in just SO MANY WAYS. I must admit that I love ice themed weapons and the Frozen Spire realistically doesn't deserve to be called the "worst melee weapon", but it is easily the most disappointing one for me, personally. They could have done so many things with it, like describing it as being double bladed and giving it a bonus hit rate flag (or honestly just saying it was short and lightweight like the Naleen Spear), having it increase evasion due to how light it would be by being made out of ice, and AT LEAST giving it the "penetrating" flag for no other reason than because IT'S A SPEAR.
And finally the Chaingun is here because it's worse than the Aegis Light Machinegun in every way. Literally every single way. It's an end game weapon that has no reason to exist whatsoever. It has 1 less damage, 4 less accuracy, the same evasion penalty, the exact same flags (aside from not being a rifle, which doesn't affect anything) and no bonus to shields. You can get both of them around the same time realistically and there is just no reason to have a weapon be so similar and yet so objectively inferior within such a close proximity to each other. Yes, you do get the Chaingun one planet earlier, but I don't think that excuses the fact that these two nearly-identical end game weapons exist in such a state, especially when both of them already rendered completely useles in the face of the ridiculously overpowered Saurmorian Railgun, which you also coincidentally get on Uveto. They should have something unique about them to differentiate them at least SLIGHTLY from each other, but instead we get a downgrade of a downgrade. It's tragic.
Honorable mention goes out to the Lash Cannon for being so hilariously awful compared to the Dancing Flashblade. It actually would have been awesome if they significantly decreased its base damage and gave it a unique perk that let it perform a bonus hit up to TWO additional times because it says it shoots out three beams of energy in its description, which would have potentially given ranged energy builds a way to compete with ranged Mercs and their 4-shot Saurmorian Railgun, but no. They don't even give it ONE bonus hit, which makes it completely useless while its melee counterpart becomes so ridiculously strong that it can actually compete with KINETIC melee weapons for the best-in-slot option on melee Mercs, even though it doesn't even benefit from their 25% damage boost.