Most players use solo weapons which are those that allow them to work by themselves whether in a group of players or by themselves. They don't tend to work well when all used at once and can cut damage when used together. Many of these have knockback or such high damage that 4 players aren't needed to kill one monster, this can lead to players wasting charges and knocking things out of other player's attacks. These weapons are tend to include Pulsars, Autoguns, Blast Bombs, and several sword varieties.
Pulsars/Brandishes (push enemies out of allies pulsar and other attacks range)
Autoguns (one charge is often enough but when a Trojan or big enemy shows up everyone tries to get a charge attack when it would be much safer to cover one knight from the smaller enemy attacks while he gets the charge kill)
Blast Bombs/ Leviathan Blade (knocking enemies around makes it hard for allies to predict enemy movement)
Swords (Constant pushing enemies makes getting a charge to hit for some very hard and risky)
Team weapons are ones that work best in a squad of knights, working together they can incapacitate enemies and deal heavy damage. These weapons require trust and cooperation, something that is hard to achieve in groups of random knights. The weapons typically used have High Flinch rates, light or no knockback, and high status chance. Such weapons include:
Catalyzers (high damage and flinch on charge makes this powerful on teams)
Haze Bombs (Keeping enemies dealt multiple statuses)
Spine Cone lines (high flinch rate on soft bodied enemies)
Shard Bombs (High Flinch with access to all damage types, with a squad you can cover large areas with shards)
Dark Retribution (high damage and large area coverage)
Cutters (Spread poison with DVS or Flinch-Lock with WHB)
Tortofists and Heavy swords (these two pair well since 2 knights can launch Tortofist charges while the Heavy sword knights position the enemies under and into the shards)
While I would agree that certain weapons are better suited for playing alone vs in parties, what I believe to matter most when it comes to party efficiency is the strategies that you are using with your weapons and the overall strategy that your party is going for.
Different types of damage
If we all bring dread venom striker, we'll have loads of up and personal damage, but for the most part only one party member can be attacking one enemy at a time. If we had a gunner present, we could then have one person dread venom strikering them for high damage and one person adding additional damage with their handgun.. a far better combo than nothing but dread venom. The same goes for a lot of the weapons you mentioned- if we all bring autoguns, then we'll do a lot of damage, but if one of us brings shivermist buster we'll be a good deal stronger because of it. Brandishes and most medium-AoE high-damage swords are the same way- bringing them alone is good, bringing them with vortex is better.
Synergy dependent more on play style
Now extrapolate that a bit and consider a party of two people, each wielding two of the "bad party" weapons. Say, divine avenger + polaris on the first party member and Blitz needle + nitronome on the second. If they just go out and spam, then exactly what you're saying will happen and they'll step all over each other. But they do have complementary kinds of damage and some of their weapons do have synergy-
Nitronome: Huge area + medium damage + med range
Blitz needle/Grim repeater: Single target + massive damage + short range
Combuster: Med AoE + high damage + short range
Polaris/Permafroster: Med AoE + Moderate + long range
The party members just need to cooperate to make this work- if I'm the combuster+polaris member and I notice that the nitronome+blitz user is trying to blitz a trojan, I should either try to use my combuster to fight the other side of that trojan so as to distract it, or I should polaris the zombies away from them so they don't take damage. If I'm the nitronome + blitz needler and I notice my friend trying to combuster a small clumping of zombies, I should charge up blitz needle to finish them off as opposed to nitronoming them away.
Beyond that though, we should both know what the game plan is for larger areas. 12 mecha knights spawn at the end of an arena. Since step one is always the menders, we can either use nitronome with permafroster to knock away mechas and safely shoot the mender into a corner and destroy it, or we can abuse maskeraith's invisiblity to blitz needle/permafroster the mender to death from an odd angle while the other party member acts as a distraction.
An optimal solution
On the bulk of levels the easiest solution to the issue of requisite synergy is to bring weapons like brandishes, drivers, autoguns, dark retribution and dark briar barrage. These are weapons that work well with themselves and other weapons- brandishes are mostly charged or focused on single enemies, drivers allow for safe+high damage at a distance, autoguns provide for extremely high damage to take out single targets when required and dark retribution/briar barrage allow bombers to deal high damage without bothering their team members.
Compare this to bringing say, neutralizers. In a party of the above weapons, enemies are going to be dying left and right to high damage attacks, and you've got to do the funky chicken to deal damage. Once you do manage to build up the shots and detonate them it's rewarding, but then so is just brandishing them into oblivion, spamming dark retribution, or firing off a nova driver charge at the right angle. Hence, neutralizer is what we call a "garbage weapon".
In the end, we see players get around learning how to use their weapons with one another by abusing weapons that almost always work well together and alone. The only problem with becoming overly reliant on these sorts of weapons on an individual basis is that it's not actually optimal in the grand scheme of things and not having to learn teamwork detracts from the game on the whole as well as the player's ability to play the game.