So far I gotten 9 or so legendary engrams and all of them except one contained a rare item, the other one contained an uncommon item.
The only time I've gotten legendary gear is from the rare engrams or the trade venders and it's make it a pain to level up.
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The cut off point in you title thumbnail is really working against you, but yeah I agree, better drop rates for legendary weapons in legendary engrams and lower drops rates for them in rare engrams.