Even Janna with DH is a thing now...

I mean look at this(match from my other account). We had a Janna/Karthus premade bot with Dark Harvest.

She first blooded Yi before minion spawn invading his jg just with Karthus( I was on the other side of the map as jungler). And by mid to late game 1 charged up Q would do 75% of a squishy's HP bar.

If a support champion with 2 damaging abilities and mediocre ratios can do this, it's obvious why DH is a problem.