Can anyone tell me what S, A and B stand for?

Super, Average and Bottom tier?

It's been nagging at me for ages..

As I don't know what they mean i'm going to create my own parameters for this list.

Top tier (Essentially overpowered)

Shaman.

High tier (Highly effective classes with an edge over most others)

Gladiator, Warlord,

Mid tier (In a good place, maybe need a little tweaking in areas)

Aramashu, Shinobi, Raider, Nobushi, Peacekeeper, Centurion.

Low tier (Classes that need tweaking and more options)

Orochi, Valkyrie, Highlander, Shugoki, Lawbringer, Warden.

Bottom tier (Trash classes that need a rework)

Berserker, Conqueror, Kensei.