According to Destiny Tracker, I have played 76 nightfalls and 140 heroic strikes since the Warmind DLC dropped. That are 216 strikes total.
I haven't got a single catalyst from these.
Either the strike catalyst drops are bugged, or the drop rate is idiotically low.
WTF.
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Got my first strike catalyst (merciless) a few days ago and im about rank 60 with vanguard. Dropped from chest in the Worm God strike.