Facebook's real moat is it's massive user base not it's ad revenue, even losing 25% of it's revenue would not have effected or killed Facebook, Only building be

Facebook's real moat is it's massive user base not it's ad revenue, even losing 25% of it's revenue would not have effected or killed Facebook, Only building better viral social network could have killed it. Ad revenue is just a side effect of this massive moat. Just like Google can survive a temporary year or 2 of 25% drop in revenue if their search dominance continues or increases but not opposite.