bitcoin doesn't have call data, it has scriptsig. calldata is a term from a malicious premined scam that has never had decentralization nor any relevance to smart contracts, just misuse of the terms.

trust assumption with just 1 honest operator is same thing as trusting just 1 guy as any number of parties can collude to become a single party, if a system has any way to profitably collude to control something undesired it's not decentralized, not even a tiny bit.