1.
Characters can't use haki with sea stone cuffs on
As soon as Luffy got his sea stone cuffs removed, he was able to use haki:
Yamato used haki with cuffs on, which makes them
not sea stone
2.
Luffy was
able to use haki while touching them and
destroy them,
which makes them not sea stone because Luffy can't use haki while touching sea stone and sea stone is said to be
indestructible
Even someone like Shiki couldn't escape sea stone cuffs and had to cut off his limbs
Big Mom had do ask people to unlock her sea stone cuffs
Same for Kaido. He had to ask people to unlock her cuffs. If he could destroy them, he would've destroyed them himself
The whole imprisonment system gets thrown out out of the window if characters can just use haki, destroy sea stone and escape imprisonment
3.
No, Luffy's collar in Udon
was not from sea stone. It was just a regular
steel collar. That's why he was able to use haki with them and destroy them
4.
Yamato's cuffs were exploding cuffs. How can they explode if they are sea stone? Sea stone is
indestructible, they wouldn't explode
5.
Yamato never mentioned anything about Sea Stone. She only mentioned that they explode
You literally have to ignore
the whole story to take Vivre Card statement as true.
It's just a cheap merchandise made for a consoomer with no brain