I haven't played this deck but I have faced it many times. The cards you mentioned are win conditions for this deck. I've seen people getting 3-4 Fireballs from Archmage Antonidas. You need to draw Mountain Giants as soon as possible.
Also a little tip for Conjurer's Calling; never waste it on a 2-drop for the sake of tempo. Somehow it's kind of consistently summons Doomsayer.
2
Any replacement for Flobbidinous Floop ?