I disagree with Shadowood - we can't have many more pirates. The game needs to have more "traders" than "pirates", or it breaks down!
Apart from that: If a "trader" is a player with 400+ ships, mainly trade ships, who do NOT plunder others except for retaliation, and a "pirate" is a player with max 5 fleets, ALL of which are mediocre or small combat fleets (no trading ships), and gets his main income from plunder, I'd say the following:
The traders will, on average, make more gold each day than the pirate. Which, I think, is necessary. However, the smart pirate may be able to make a decent amount of gold, too. The traders may think it "unfair" that the pirates so easily can hit them (they have, after all, lots of ship), while it's more difficult to hit the pirates back, but they need to remember that even without hitting the pirate back, they will actually usually earn more gold than the pirate - on average. That said, there ARE ways for traders to defend against such attacks, and it IS possible to hit pirates. It's just expensive.
I think the "problem" is that the traders - the BIG traders - cooperate too much (they are in large guilds, and the large nations all have agreements on who is to control which port). That is, of course, an advantage for them; they make more money this way. If, however, there were more competition among the traders, there would be more "action", and perhaps more hybrid players, but also less profit for the traders, of course.