The Essex is incorrect in game.. but mainly because of game engine limitations. The real USS Essex had "Saddle" guns on the bow. These guns would be turned to fire as bow chasers when needed, or fired as part of the broadside. It also had 2 9lb guns on the forecastle as chasers.
The only thing the Essex has over any other 5th rate, is it is the most maneuverable 5th rate for the weight of firepower. It can easily turn inside a Leda, or the Endy, or even the Indafat. It has decent armor, and great points of sail giving it the most flexibility out of all of the 5th rates of its class.
While the Leda is faster, it also heels FAR more, average heel on the Leda is around 4-6deg, exposing its much thinner underside. If the Essex ends up on the inside line it can easily point all of its guns at the waterline of the Leda and sink it without even a second thought.
The Essex brings one thing to the table that no other heavy 5th rate has.
Handling.
The Essex sails like a corvette, it can out turn the Trincomalee, Indefatigable, and the Endymoin with ease. It is only marginally slower than the Trincomalee, and faster than the Indefatigable by a far amount. The only thing that handles better is the Pirate Frigate, and that is slower and has less firepower.
Not to mention the Essex has a better all around sailing profile than any of the other heavy 5th rates. So when you are looking for a Jack of All Trades, the Essex is the ship you need, but it is also the master of none.
There is no one thing the Essex does great, or any one thing it doesnt do well at.