Even back in its healing days, dome was never a popular spell. It needs to be different than shield and right now there just isnt much differentiating it.
My idea is to take away the cost per second and change it to fixed cost. The dome would stay up once cast for a fixed amount of time, making the wielder invulnerable to projectiles like shield does. Traps would still do damage.
It could be a good tactic against someone lightning baiting or missle spamming, or prison/dragon breath. Basically you trade the utility of shield for mana effiency (popping shield repeatedly drains mana quick). Another great use would be protecting yourself while killing a demon.
With appropriate mana cost and time duration i really think this could work. If it is too cheap it will be overpowered. If it is too expensive it will be useless as ever. One possible way to balance would be take away regen during dome time. That would make it harder to spam dome all match. My initial number ideas are 30 mana cost for 10 seconds use, no regen during. Or 25 mana cost, 5 seconds use and regen during.