On Rav Elyashiv’s Teshuva…
Rav Elyashiv’s Teshuva is NOT in relation to EVIDENCE for murex. The question posed is:
(1) חוקרים claim this is the Chilazon and (2) there’s nothing to lose — therefore should we wear this dye?
No evidence for or against murex is presented!
Indeed, the response relates to the question of נאמנות החוקרים where past theories were refuted (and some other צרופים).
It’s very well known Rav Elyashiv spent his time on Shas and Poskim and was generally not the kind of posek who researched the technical aspects the Shailos — that is something Poskim the like Rav Belsky do. Instead, Rav Elyashiv’s approach was to respond precisely to the question how it was asked.
The cogent evidence for the murex, especially as has been developed lately, is a highly technical question never posed to Rav Elyashiv.
Regarding Rav Chaim Kanievski, in a lengthier Teshuva in a footnote in Da’as Noteh, he states that his position is based on his Rabeim who didn’t wear this Techeiles. Presumably he is referring to those who lived after the murex was a question, ie Rav Elyashiv.
IMHO this is a very, very technical shaila, and people should be relying on the likes of Rav Belsky.