With the game being out in Korea for so long, it's a given that the Western Release won't have the entirety of the content immediately upon release. One part of that is the classes, still unavailable in the West.
The first class missing in Lost Ark, currently, is a warrior advanced class called the Destroyer. A pumped-up version of the BErserker class, Destroyers use giant hammers, coupled with heavy armor, to deliver massive Area of Effect attacks that contain crowd controls effects. It's an incredible frontline class, capable of holding quite a few enemies at bay.
The next one is the Lancemaster class, which is a variant of the Martial Artist class. the main feature of this class is switching between two weapons, with each of the two having their own combos to perform, and things they excel at. The Lancemaster class is one of sweeping attacks and long combos.
Bringing sci-fi onto Lost Ark, we have the Scouter class. This one is a subclass of the Gunner main class, one of extremely high mobility, and with a potential for high damage, all the while filling up its bar which allows it to don an exoskeleton suit, to deal even more damage.
No MMO is complete without a Summoner subclass. Lost Ark is the same, with their summoner subclass being a variant of the Mage class, allowing players to summon various elemental creatures to fight in their stead.
If you want to play a mage, but find the usual playstyle of that class boring, the Arcana Mage subclass is for you. this is a special variant of the class, centered around doing card magic, with each card pulled from the deck having its own special effect.
Lastly, Lost Ark has a brand new main class called the Specialist. Currently, there are two subclasses available with this class, one of which has only been teased even in Korea. The one that is currently live, called the Artist, has incredible visuals, and is a support-type class.