New Katarina to stronk or Abys to weak

So I've been playing against the new Kat more recently, and iv noticed that Abys Scepter doesn't seem to mitigate her damage in the slightest. In fact I just finished a game were pre 6 i had a negatron cloak, all she had was boots 1. and she was shreading me completely. I kept building til I completed the Scepter but at no point did it stop her or even slow down her damage. How can i have stacked MR and it be completely useless against a Kat with absolutely no offensive items. Honestly, as odd as it sounds, it seems like the Scepter is just a waste of gold. I could have spent that on an offensive item and at least would have been a threat.