The drop rate differences between normal and heroic strikes is completely neglible. I actually had more luck with the normal strike playlist. About 3 keys in 16 strikes, which is more than I would have gotten through heroic, and in less time too if I had run the same amount of heroic strikes.
With the amount of RNG involved in everything in destiny it's hard to make such a definitive statement. I was just speaking from the experience the community has with strike drops. And even then people argued about drop rates after like an entire year of strike exclusive drops and shitty droprates. I got back to back keys in 2 heroic strikes, doesn't mean the drop rate is significantly (or not) higher than normal.