my question was if the blockchain is retrieved from a central location (eg dropbox, bitcoin foundation, my http server) if it is still verifiable in a trustless manner.
No, verifying one full archival node with many pruned UTXO full nodes is not sufficient enough. It could work, but at the expense of security where the full content of those archived blocks could be manipulated.
that still doesnt answer my question.
may i ask why it is not enough to secure the blockchain that way?
i assume that all miners already have full blockchains and we are only talking about new nodes (old nodes already have/had the full copy and therefor a validated utxo)
new nodes would still connect to running nodes - they just wont deliever all old transactions. blockheight, headers and pow is still all the same.
i fail to see a way how a new node could be tricked or has lower security if all old transactions are obtained in a different (even centralized) way