Romantic/historical pirates were MUCH more of an impact and relatively more powerful. They impacted trade routes, forced countries to arm merchant ships or use escort vessels , and in some cases held forts or mini-countries. A pirate might also control several sizable, combat-ready vessels.
The pirates of today are simply kidnappers with boats. They only have any success because their prey has refused to implement any significant defensive measures. Unless pirates get to the point of having something like PT boats that can threaten a small/medium combat vessel, they're nothing like on par with historic pirates.
The only category where modern pirates might have an edge is impact-per-man or per-dollar. Today a few dozen criminals with a fishing trawler (mothership) and some fast boats (ribs or otherwise) can capture a vessel hundreds of times their size. However, again, this is just because the target vessels don't bother to arm themselves. If you threw a squad of trained mercs with assault weapons on every sizeable transport vessel in dangerous waters, piracy would be reduced to preying on small fishing boats.
On the tin. Which is more effective for their time, the modern pirates of our time, such as the Somali pirates, or pirates during the Golden Age of Piracy? Which was more of a factor of their time and which group as a whole was more effective at what they do?