That is a bit lazy.
One was a mechanical being and the other one is cursed. Why should there be a Samurai alive for 800 years. I am all ears.
Cuz every SH is an Enemy of something that brings Sadness
Such as Hunger, Weakness, Poverty, Sickness, Racism ... etc
Their Dreams gonna End such Problems
Luffy as their Captain is Leading them towards creating this Joyful World
But what will He personally End? It's Death
Joy Boy being First Pirate means He was First to carry a Jolly Roger
Hiriluk explained what Jolly Roger Means, it's about facing the Impossible
And then you add on Top of it what you put your Faith in that can help you overcome such Impossible Obstacles
In Hiriluk's Case, He Put Cherry Blossoms
I don't know how Joy Boy's Flag looks like, i don't know what's his Version of Cherry Blossoms
But He invented the Skull Flag, otherwise He wouldn't be First Pirate
So his Definition of "Impossible Obstacle" is what the Skull directly represents "Death Itself"
So Joy Boy's Journey was about finding a Solution to Death, so that no one suffers it anymore, just like SHs Dreams will solve Racism & Disease & Hunger ... etc
Seeing Zunisha & Emet, it's obvious to me that Joy Boy Partially Succeeded, meaning He found an Incomplete Solution to Death, and no wonder that it was used on his Crew, but apparently They are made to Die once their Purpose is Fulfilled, so it's not Perfect Immortality
Another Hint at this is that Hiriluk's Farewell Chapter was called "Snowy Tale", similar to Joy Boy's "Laugh Tale"
And it was named due to Hiriluk's Kingdom being covered in Snow, but why Snow? Cuz Hiriluk wanted to turn Snow to look like Cherry Blossoms that can heal everyone like it once Healed him (Or whoever He was telling a Story about)
So Joy Boy's Story being Named "Laugh Tale" means that Joy Boy's Kingdom was covered in Laughter (Just like Jaya & Yasuie Town), and his Dream was to turn Laughter into something that doesn't allow People to Die, meaning as long as you Laugh, you will never Die
Hence why Laughter is associated with Death a lot in One Piece, and i'm sure you're aware how much Laughter is Symbolic in One Piece.
Based on all this, i believe that Joy Boy Crew were Temporarily Protected from Death, but Unfortunately not Permanently
Emet died the moment it fulfilled it's purpose, and Zunisha gonna also die when it finally reaches it's destined place, and imo this Samurai is also waiting to fulfill his purpose, so that He can finally Die
First Vander Decken was also teased to have being cursed with Immortality, so He might have been Joy Boy's Jinbe
And i won't be surprised if Elbaf King is also 1000 Years Old, and Portgas D. Rouge was Joy Boy's Nami ... etc
Oda clearly doesn't mind bringing Characters from Void Century (He also did it with Imu & Toki)