I believe that too about it being for their new allied race gimmick; I myself hardly even visited the forums in the 13 years I’ve been playing until I pre-purchased BFA early on and had the requirements met to start leveling a Void Elf Warlock and it was then that I found out about the XP nerf and I’ve been a voice on the forums ever since.
I honestly believe they knew players would be wanting to level these new races and intentionally slowed down the speed we could level so that they could earn more in subscription time and for the ones that didn’t care to level could just pay for a boost for $60.00.
What gets me is they slid it in with patch 7.3.5 and nothing was said about it being intentional until here recently when a Community Manager admitted to it which can be viewed here:
So as you can see all the way from Feb when this thread “XP FROM DUNGEONS” started by a Community Manager from Blizzard themselves asking for feedback from us players until November 29 2018 no one from Blizzard commented about the “XP” loss we were complaining about when a high level ran lower levels through dungeons “Power Leveling” which had been going on for 13+ years, It took them this long and over 4600 post in this thread before they admitted to us that it was indeed intentional.
Oh also just so everyone knows there were a whole lot more views and likes on this forum before the new forums started, The likes and views just weren’t carried over to the new forums.