I check my alts that I haven’t leveled in Remix yet daily before heading to bed. The XP percentage gains as well as all other transferable power are absolutely transferred. It is transferred at a level that appropriately matches the alt’s current level and AP progress, just like it was in MoP Remix. Nothing about that has changed. Maybe you are just not looking in the right place. There is an icon in the buffs area called “Infinite Power”, which lists out the percentages. But an alt that has not progressed through anything yet will not receive the same amount as a main character who has done all the work. This is no different than MoP Remix was.
Still having a lot of fun with Remix. Finishing up Suramar today, day 2, and just got my “Balance of Power” final quest on my Druid, the one from Kalecgos and Senegos and predecessor to the 50 motes you have to collect in the Nightmare raid.