As an example, something extremely obvious with another class counterpart is Necromancer vs. Conjurer. Necro gets a bunch of disease/death spells and undead/demon looking pets, whereas Conjurer is all elemental spells with significantly different looking elemental pets. I understand the mechanical differences of Swashbuckler vs. Brigand in that Brigand is single target, Swashbuckler is AoE, so now I'm wondering about the thematic/aesthetic side, if there are any differences. Anything on the "Just for fun" or "for looks" part of a class, basically.
One is a pirate and one is a thug. One is aoe dmg/aggro transfer/debuffs and one is single target dmg/stuns/better debuffs.
Swashies also have great debuffs for the mobs offensive skills and some magical defense debuffs. Brigands are all about defensive debuffs, especially Physical.