Does that sound reasonable? Were cargo ships being built in less than a month's time, continuously for 550 years? That's some serious manpower and material procurement. And that's just for the ones that sunk in the regions around Portugal?
I'm skeptical. Not saying it's impossible, but just that it sounds excessive by a considerable factor.
I think the numbers of sunken ships is reasonable. In the age of sail wooden ships were much smaller than freighters today. A typical Spanish galleon was 100-150 feet (30-45 m) in length and 40-50 feet (12-15 m) wide (the preferred ratio was 3:1 or 4:1). If you have smaller ships you have to have more of them to move cargo.
Also sailing ships depended on the wind to move and often the wind, even without a storm, would remorselessly drive these ships onto rocky shores to break up and sink despite all efforts of the sailors. Sailors called shores where conditions were likely to drive their ship onto the land a lee shore.
A lee shore, sometimes also called a leeward (/ˈljuːərd/ shore, or more commonly /ˈliːwərd/), is a nautical term to describe a stretch of shoreline that is to the lee side of a vessel—meaning the wind is blowing towards land. Its opposite, the shore on the windward side of the vessel, is called the weather or windward shore (/ˈwɪnərd/ or, more commonly, /ˈwɪndwərd/).
Because of the danger of being driven aground on a lee shore it is essential seamanship to treat one with caution. This is particularly the case with sailing vessels, but a lee shore is an issue for powered vessels as well.