I’m consistently getting a 65-72% win rate after each session.
This isn’t far off from any other Rainbow/Mining Mage. I’ve noticed too many Mage decks are dropping in win rate percentages, but that’s because they’re moving back to Arcane Artificer. It’s not a bad card. It’s just not great in the meta.
The wonderful thing here is that most matches aren’t determined by Sif at all. Tempo is important.
Queen Azshara serves as a flexible tool to transform you into whatever role you’re playing in that matchup. Ring of Tides gives you a 3rd copy of Elemental Inspiration or Wisdom of Norgannon . Horn of Ancients is probably the least used option, but knowing your colossals outs is important. Xal’atath acts as a mini-Sif. Tidestone will fill your hand back up and random Mage spells tend to give you more discover and card generation, perfect for long matchups.