It's not really a challenge. VT-IT+ hit you less than half the time, or you're gearing poorly.

WoE is barely an event and you might as well not go if you're not a Summoner, unless you want to spend most of the time weakened.

And it is comparable. Just like you should have brought a real melee instead of a RDM, if you needed heals, you should have brought a mage. There's just no need for DNC to help heal.

Yes, you can do it (albeit, mediocrely) just like a RDM can melee (mediocrely). Just because you want to do something doesn't make it useful.

Additionally, mages just don't need help. Any situation where they're struggling to keep up, you'd be better off tossing a BRD,COR, or additional mage, instead of a DNC.