Could an unprotected cruiser still count as a warship?

Can a ship that destroyers could readily defeat really be called a warship?

Yes, because warships can serve limited roles, and the comparison also reveals that Spain and Britain developed the destroyer idea at about the same time.

The prompt argues that a vessel easily beaten by destroyers looks more like a patrol craft or courier. A limited combat role can still make such a vessel a warship. The Spanish torpedo-boat destroyer Terror accompanied the force across the Atlantic, so destroyers were already relevant to the comparison. Spain had reached a destroyer-like concept at roughly the same time as the Royal Navy, illustrating how several navies can independently converge on the same operational solution.