They've made shields so OP, it would be foolish not to use them most of the time. They should buff staves so it increases dps more dramatically. Rangers kind of have that... dual wielding gives you more dps. So they should probably add talent that increases your spell dps when using staves to balance it a little bit.
From D&D point of view the spell casting + shield isn't something new - Cleric class, battlemage or perhaps necromancer for example, but it always comes with disability to cast certain spells or limited damage.
Ranger + shield on the other hand is kind of nonsense.