I don't know where people are getting this "Only tanks and healers would get upvotes." I've met plenty of players who are pretty bad at both, and we barely scrape by in the run thanks to a DPS spectacularly finishing the boss off in time.

Speaking as a Paladin main: Tanks and Healers are not infallible and there are some pretty horrific players playing them for fast queues. I'll gladly give my upvotes to a worthy DD.