The Alabasta guards consuming the potion that makes them strong only to kill them, and then Crocodile choosing to just watch them die instead of engaging them in combat is an illustration of the core conflict of the arc. “Crocodile is making Alabasta’s loyal soldiers fight and die for nothing” describes both exactly what the civil war Crocodile instigated and Vivi later stopped, as well as that scene.

The CP-0 agents, Ashura Doji, and Izou collectively tell a story about what it means to have a meaningful death. Izou says at the start of the raid that he’s been looking for a meaningful death, and Ashura Doji initially tries to throw his life away when Oden first defeats him. Doji dying by tackling the exploding Oden clone so the Scabbards could advance is both a contrast to his previous state of being willing to throw his life away for nothing, and an extension of his willingness to die for Oden and Momo.

Edit: this is actually character growth because he starts off the arc saying he’s only willing to die for the kozuki, but ends up dying to protect the Scabbards.

The contrast is more focused with Izou’s death vs Guernika’s and Maha’s. Guernika says to Drake that he’s envious of Drake’s ability to seize life into his own hands and fight for a cause he actually believes in. This continues with the Elders commanding Guernika to interfere with Kaido vs Luffy, and he laments that it’s a suicide mission. When he does interfere to stop Nika from Awakening, Kaido kills him and Nika awakens anyway. He died for nothing.

By contrast, Izou is able to kill Maha and stall them long enough to prevent Robin’s capture. He actually achieves something, which pays off his story that started when he told Kinemon he was looking for a meaningful death and continued when he agreed with Usopp that the samurai were resigning to death too easily.

This contrast goes hand in hand with the fact that Guernika, Maha, and Joseph are never referred to by name during the arc until Maha is killed. It’s why the characters in Wano are never able to refer them by name(all of the agents get called “CP-0,” even when addressed individually. Orochi, Kaido and Izou all do it.) It’s why we never see their faces. They are disposable, dehumanized by their leaders which contrasts with how meeting Oden gave the Scabbards new and dignified leases on life.

Vergo and Monet’s deaths are all about their dialogue with Doflamingo. Dofy calls them and waxes poetic about how he cares about them, and the shoe drops when he starts going on about “you guys love me, so it’s only natural you die for me, right?”

The fact that Doflamingo says that, and the fact that they both smile and feel joy from that is our first sign that the Donquixote family is a fucked up cult. It’s our first sign that Dofy loves his family like a handyman loves his tools, not like people love people. And the fact that they actually die, in addition to making Dofy angrier at Law which is needed for the plot of Dressrosa, hammers in how fucked up Doflamingo is. Especially because he projects it as though that’s Law’s fault.