I've seen a few people mention you had to be 100 to get a DH, but Legion gave you a free 100 when you purchased. I think from a marketing perspective, the allied races are the big feature this expansion. It seems silly of Blizzard to lock it behind a rep/story grind of the previous expansion. I think if it were a level thing it wouldn't be nearly as bad for new/returning players as these requirements. If it were locked behind something in the current expansion, like the Zandalari and Dark Iron will be, I would say that is fine too. I understand from a Blizzard story perspective, and I actually think it's neat that people that already meet these requirements will get the races immediately. However, the people that keep the lights on are the casuals, and they may be turned off by this.
Before I get flamed, I don't really care about the requirements because I got them all a while ago.