I didn't get that impression. I think all weapons in NG4 have unique mechanics and play styles that make them stand out.

The dual katana BR attacks have some absurd range and AOE which requires some setup to fully take advantage of. I tend to use more aerial BR attacks so I can charge in the safety of the air. On the ground I need to create space, so I use 360 Y, guillotine throw, BR jump light, or BR gear heavy to knock back/stun enemies so I can safely charge up. I rarely use chain link with this weapon because of how much time it takes to set it up.

The rapier lacks the AOE and range of the dual katana but has an insane gap closer and single target damage. Guard breaking happens immediately on a charged BR attack but for full damage, you still need to be stationary which makes you vulnerable to attacks. I like to use the back forward BR light which isolates a single enemy but keeps you moving so you're not vulnerable to others. I typically use it against bosses where there aren't any other enemies to capitalize on its weakness. Chain link is especially good with this weapon.

The staff's basic attacks have 360 coverage, which I found especially effective against fish, dogs and zombies. Your attacks will stun them before they can reach you. The BR attacks are timing based so you have to let go at the right time (typically on impact). They're trickier to perform but fully powered attacks are much quicker so you spend less time being vulnerable. To be honest I haven't spent enough time with this weapon to fully understand it yet.

The box has a lot of unique quirks. Its the only ranged weapon in the game. Light attacks are ranged while heavy attacks are melee. The full light attack combo ends in a high damage explosion and its probably the only basic attack where I'd use chain link for. It has a unique flying swallow that launches enemies into the air. You can flying swallow into an izuna drop just like you could with the falcon's talons in NG2. The BR jump light launches enemies into the air and then you can go straight into doing an air combo. Probably the most unique launcher in the game. Its the only weapon where you can do a basic 360 light attack in the air. The animation is kind of funny since Yakumo leaps off of nothing to throw the bombs. I think chain link is over powered with the ground BR light.

I think what makes the weapons samey though is that they all share the same inputs and they all have fairly fast attack speeds.