Your question is about why mage is better for PVE?

Right I've some small explanation

Firstly mage is famous for it's AOE(Area of effect)
all the skills mage have are completely aoe and can hit multiple targets at a time but you one hit die sometime during elite bosses...you can have shield for this.
and the heal that mage does completely heals and it's very useful for others.

and as you said,yes Rogue has higher damage but can one hit at a time only that's the reason why it's mostly useful for PVP

this might help you.

~Prahi