Simple. You use shamans removal spells as finishers which leave you nothing to deal with the board apart from 2 storms and hoping for favourable trades. The deck is not viable in my opinion to be honest.
Idealy they'd be used as finishes, but no I'm not opposed to using them to take out problem minions too. I just prioritize minions to kill minions, and more importantly face damage to whittle the health away.
With the right combos you can take a good chunk of life away in a single turn. The way I have them set up each combo is designed to take 1/3 of the opponent's life, maybe more.
However if I do set it up to be able to use the full spell combo. BM + 2LB + 2LitB = 20 damage for 10 mana, leaving only 10 face damage minions have to do while LS and other minions keep the incoming damage on their end from piling up.
I feel like the deck has a lot of bursty potential with the right combos. Leeroy double rockbiter for instance. Doomhammer double rockbiter, etc etc.
I know the Ogre Magi might be redundant with the Azure Drakes, but they do come out faster, and they pretty much assure I always have a least 1 spell power minion on the board at any given time. In fact in the few games I played to test things out it wasn't uncommon for me to have 2 on the board to let me fire off some nice spell damage combos.
I've been a bit iffy about the nightblades too, yeah, but I just like the idea of having an (almost) guaranteed 10 face damage between those and the lepers. In theory if everything works out I'd cast 2 lepers, 2 nightblades, and then baring any healing I fire off the BM, LB, LitB combo to finish it off. Or the Doomhammer double rockbiter, or Leeroy double RB to take another 1/3 of life away.
I do agree the deck could use more card draw, but I'm not sure where to fit it in. Maybe replace the lepers or nightblades with loot hoarders? Or -1 leper/NB for a hoarder?
Mind you I'm not married to this deck, just something I came up with I thought might work in theory and be a style of play not many people would expect from a shaman