User blog comment:Willbachbakal/(Item Concept) Crowd Control/@comment-24795478-20150101132103/@comment-1330314-20150102123823

It's good that you mention, because I think she's a good example of how spell shields interact with all of the abilities you mentioned. Despite its far smaller cooldown and availability from level 1, it still doesn't let Sivir ignore Ashe arrows, or Varus ults, or Caitlyn snipes. Even if she were to build another spell shield and get Phase, she would still not be able to hard-counter CC consistently enough, whereas the current QSS can achieve that on its own. It's also worth mentioning that, in the case of Sivir following through with this, it would be at a significant cost to her to her damage output, and would allow and  to out-trade her on autoattacks alone.