It makes no sense for an exotic to be weaker than its Spirit version. Spirit of Cyrtarachne is incredibly valuable on Prismatic, because it can work with all grenades, and even Gunpowder Gamble, not to mention you get an entire other exotic perk with it. Cyrtarachne's Facade, on the other hand, only works with 1 specific grenade on 1 specific subclass. If it worked with all grenades on all subclasses, just like the Spirit version does, then it would be way more valuable and versatile as an exotic, and we'd actually see people using it outside of the occasional PvP match once in a blue moon.
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Cyrtarachne’s Facade is amazing on Strand. The fact that you don’t see that is not Bungie’s problem. Don’t get me wrong, Spirit of Cyrtarachne is fantastic on Prismatic for the reasons you pointed out. But it being good on Prismatic does not mean the OG is terrible. It just has a different utility.