I mean, the way I see it, Thaumaturges and Conjurers have both One-handed and Two-handed weapons. I don't really see a reason for them to not toss 2h swords to Gladiators. It would simply allow them access to a more potent weapon when soloing or not filling a direct tanking role.

Basing an entirely new class around the Greatsword seems like it would be kind of a moot point with the variety of DPS classes we already have.