Hi,
I found most of mine (8 so far in HC in a total playing time of about 34 hours) in level 70~75 gRifts. I seem to remember finding one while doing bounties and another one in nephalem rifts… but most of my Ramaladni’s gifts were found in gRifts.
Yes, it may look like they drop less often… and as @Kirottu explains, it kind of make sense. We’re still getting the same number of legendaries as before, but there are 2 new types of legendaries that can drop.
You may want to look at the time you need to complete a given gRift level… try to find the max level that you can complete in 2 or 3 minutes… 4 minutes max. That will give 10~20 gRifts per hour and, depending of the gRifts level, some 100 to 200 legendaries per hour.
Sometimes, you get lucky 
Best of luck in your games !