maby I am reading what you mean completely wrong but doesn't the current battle system do exactly what you said.

All the classes have aoe version of normal attacks, and solo versions.

Mages have a button to switch between Aoe/single targer modes.

Lnc has attacks that hit all mobs in a line.

Archer has aoe and single target attacks.

Pug has single target, line, and aoe attacks

Glad has attacks of all dmg types as well as circular attacks

Mrd has single target normal attacks and half circle normal attacks.