While at level 70 the list of possible drops is bigger, you can still get all the drops you need and it is definitely going to be faster to do so on a higher difficulty at lv70, rather than a lower difficulty (with low drop rates) at a lower level while also trying to avoid leveling up.

But it doesn’t seem that’s the case for you. The level of the 'low-level' Legendary items is the minimum level those items will drop at. Then say, ‘I didn’t get any ancients in all this reforges’. That, those people actually get ancients, but when the stats are bad, not what they were looking for, they erase it from the data pool. There is another theory I have with such a bad luck streak, not particularly talking about reforging but other stuff as well. I know it’s superstitious, pseudo nonsense crap, but it makes me feel better and I never had such a bad luck as you in this game or some other ones. What I consider those bad luck as is that, some stall in the programming code that prevents certain outcome to appear, and changing some variables in the game resets that process/interaction. Simple thing I do is to go to a mystic in Act 5, instead of 1 or 2 I normally play the game at. I’m not really a superstitious guy, but when some streak of bad luck happens (like what you’re experiencing now or when certain property simply won’t show up when enchanting), I try to change something in my environment in game. No, not saying this to insult you, just saying to switch some variables around you. You know what they say about insanity, doing the same thing over and over again but expecting different results.

Diablo 3 reforge legendary low level