No...You definitely cast Dreadstalker on CD.
Yes.
Who is reporting their low damage makes them not worth casting? Because that's definitely not the case. In terms of damage they do for 2 shards vs damage 2 Imps do with a 2 Shard HoG is astronomically in favour of Dreadstalkers. It's always worth casting Dreadstalker over Imps, period.
Also in terms of TKC damage they are huge as well;
Clicking on the picture brings you to the full spreadsheet.
2 Dreadstalker = 250% damage gain on TKC, 2 Wild Imps = 94%.
In short, Dreadstalkers are good.