I’m not sure why this should be nerfed to 3 mana. It’s basically all the control mage sustain in one card. Control decks like priest warrior and dk have plenty of sustain. Mage on the other hand is one of the few classes that rely only on armor and barriers (ice block, solid alibi) for sustain over heals. And that beautifully defines the mage class as a whole. Making basic sustain for mage difficult for me it’s not a great choice.
For me it is 800 free dust. 
I still think the main problem is not solid alibi itself… the problem is the amount which can be used by a mage in a match… recycling, discovery… that is the problem. Now everyone switched to OTK shaman. 