I have played 14 vanguard strikes in a row and used 15 ToC and only had 1 exotic drop, I never had a single exotic drop about three weeks ago when I ran 20 vanguard strikes and used 20 ToC, that's when I got fallout 4 and stopped playing destiny...until I heard about the SRL, amazing but rewards are still RNG, I mean really you come first place and you still have to play the lottery. Sort it out bungie.
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There's a cool down for them before and after you get you're exotic engram.