“The Spanish attempted to limit this export of silver by limiting the number of galleons. This resulted in the building the largest ships the technology and materials allowed.”
Government regulation even then.
Spain had a complex web of regulations and tax laws applied to different parts of its vast empire in the New World and the Old. Trade with the New World vice royalties was very tightly controlled and heavily taxed. Spain was the first truly global empire and its rise from a handful of poor feudatories in the north west of Spain to its zenith in the 16th and 17th centuries is a fascinating and sobering narrative as the great empire then began its long downward trajectory that would end in 1898.
Yes, I believe their CAFE standards required at least 3000 miles per galleon.